While we're on the subject of dungeons and treasure, as we were on the last post, I might as well bring up a salient point.
Why would monsters have coins at all? This is a serious question. The coins aren't worth anything to them of themselves. They can't be eaten; they serve no immediate function so long as they retain the shape of coins. If the monsters were intelligent enough and liked the metal, surely they would have hammered down the gold into shapes of convenience or delight to them, as our very distant ancestors did with the gold nuggets found in streambeds.
Think. You're an orc, you've got a strong hate on with the world - that depiction of 'evil' we take for granted - and you can recognize that the figure on the coin is that of a HUMAN. In effect, something that sickens you to look at. At the very least you would use your hard metal weapon, or two heavy rocks, to pound out an image that disgusts you. It would be like keeping an image of Hitler or Lady Gaga (obviously the logical reincarnation) in your pocket (if you like, insert anyone who truly, honestly disgusts you).
Now, you might tolerate it if it were worth something. If you were in Saudi Arabia, say, and still felt sensitive about the destruction of the Two Towers, you might not like the images on the money there ... but you'd go on keeping it because it IS money. You need it to buy things. But an orc doesn't need that coin to buy anything. It can't go to the market ten miles away, plunk down its coin and buy a sack of green leafy food ... the sort it can't get at home. (Arguably, an orc might be allergic to green leafy food - who knows?)
Once the image is ruined, so too is the coin. No reputable clerk would take it from you. The point of the image on a coin is to prove that the item has the value it says it has. A lump of hammered 'gold' could be anything. It could be 90% copper. No one would accept it for trade as a 'coin'!
More to the point, how is it presumed the orc gets the gold coins in the first place? It steals them. Yes, that's right, the orc and his buddies roll into the local village, kill a few peasants and guards, plunder the gatehouse and ... march off with 40 lbs. of heavy metal that serves no purpose for them.
Um, logical? No, not logical. At the very least, they'd probably be more interested in the copper than the gold, since it serves to make good pots and other kitchen utensils. But gold? Well, its pretty, but if it comes down to a sack of gold or a haunch of horsemeat, I think we can figure out what the orcs really want.
It gets even less logical for creatures further down the dungeon scale. Maybe the orcs might want the gold to pay off a group of local bandits who, in the daytime, roust anyone approaching the dungeon entrance. But what is the troll four levels down keeping it for? My best argument might be that the troll uses the money to pay off parties, in the sense of "Take my money, leave me alone." The strategy has a long history of success with kings and princes. Apart from that ... we're back to the fact that it would be hammered into shapes unrecognizeable ... pieces of jewelry that the trolls might enjoy but which people back in town probably would not.
Yesterday I made a joke in the comments field, in reference to the many desperate suggestions to explain why wealth would not all be found at the bottom of the dungeon. I said, why not just assume there are fountains of gold at every level? I'm stunned that no one jumped in to yell at me that gold and silver mines are exactly fountains of the kind I suggested.
But what reason would any creature have for mining gold and silver, if they had no contact with a trading economy? The Dwarves of Moria would probably have the option of dealing their gold and gems with the surface cultures of Middle Earth, though they might hate to let go of their gold - which makes no sense, culturally, since the only purpose to having gold in large quantities is to get rid of it for things that keep you alive. Granted, I have no idea how a dwarf's mind works. Or a dwarf's biology. It's a mystery to me that they don't all die of rickets and scurvy long before the arrows get them.
If you're a troll or an ogre, however, or something more fearsome like a beholder ... what the hell is the point in all this coin? I might grasp a ghost or a lich, keeping this hoard of gold out of a twisted sense of nostalgia ... but for races that just keep the gold out of sheer hatred for the surface creatures, why keep it in pristine fashion, so that without any modification AT ALL the surface people can come pick it up one day and spend it at the Medieval Mall the next? Does that make any sense? Wouldn't it be more satisfying to transform all the gold coin into paper thin squares and hammer it onto the walls of the cave, as many religions have done throughout history with gold that actually meant something to them? Imagine a party being told that yes, there's the gold of 50,000 coins here ... but it is all less than a tenth of a millimeter thick covering all the walls of the gnoll's cave, and it will take several lifetimes to scratch even a third of it off.
There might be some kind of spell that would make it easier.
In short, I'm saying that if you really think about it, even the 'coin' that sinks to the bottom - along with a lot of other treasure, using these same distinctions (what purpose would a beholder have for a gem?), would simply cease to be.
I know that someone's going to say that adventurers would drag their ass into caves, die there and leave behind piles of treasure that could be found by later parties ... since the monsters wouldn't have any reason to disturb it. Yes, but you see, they would have reason. If there WERE creatures roaming around in the underworld, eventually all the gold and iron there would have been consumed by the things that eat gold and iron; the gems would be picked up, skipped on ponds and lost; or collected by gooey things that dragged them along for months before pooping them into a crevice or a river; or deliberately smashed by not-so-intelligent but hateful creatures. Destruction is much more fun than treasuring something, and if you're arguing these creatures are EVIL, then destruction is de rigueur.
Unless they're not evil ... in which case, why wouldn't a trader do business with them, and bring peace to the world? Come to think of it, even if they ARE evil. Why wouldn't a trader do business with them? Have you met a successful trader?
(Please, for the love of heaven, don' t think that justifies monsters keeping coins. It would only mean that a monster's lair wasn't any more coin-heavy than a peasant's hut).