Filling aquarium with stones on the ground

I’m trying to fill a aquarium with stones on the ground. I’m not sure if this is the best way to do it, but that’s the only fast way that came to my mind. Currently I’m trying to fill it with a fluid particle system, where the particles emit an object. I never used particles, so before I dive more into the particle system here, I’d like to get your opinion if this is the best way to do it? First I was thinking about a displacement map but I guess that’s too complicated and won’t look like real stones in a close-up.

Here’s how I would handle this. Start with a low poly stone (e.g. a simple icosphere). Create a cube for the bottom of the aquarium, scale it very small along the z-axis. Add a Particle System. Set the type to Hair, and check the Advanced box, then under Emission, set Emit From to Volume. Under Render, uncheck Emitter, then choose Object, and choose the stone as the Dupli object. Play around with the size, random size, children, etc. until it looks the way you want.

But with Zodiac’s method you might get mesh intersections if they are too close which will look nasty if the rocks are larger.
Instead, a good (cumbersome) way would be to create several rocks with rigid-body solvers on each, then duplicate them in the space above your container many times. Set your container to affect collisions (all this is in the BGE settings) and run the game engine after enabling rigid-body to IPO record.

I was thinking the same first, but was going with particles because I was afraid I might run into performance issues. After all I’ll need thousands of stones. Particles should be mostly instanced, right? zodiac’s method works fine, with two exceptions. First the childen particles are intersecting, second the children particles are outside of the cube mesh (outside of the volume). Looking for a way to fix this right now, but if you know a solution, I’d be thankful for a solution.

If you bulk out the box with another that nearly fills the bottom you won’t need so many objects?