A while ago I was looking in aquarium shops for a new decoration to put in the tank, but most of them seem to be mass produced and I wanted something original.
So, after visiting my parents house and raiding their back garden (they think I'm a looper) I came up with the following idea:
1. I took the rocks home and boiled up in a pot to get rid of dirt and any creepies.
2. Poured some vinegar on the rocks, to make sure they were safe to put in the tank.
3. Using clear silicone sealant, glued a number of small rocks together (this took a while, because due to the weight of the rocks I had to glue a couple, wait 24 hours for the sealant to dry, glue a couple more and so on...).
4. While the sealant was still quite tacky between the rocks, I added a few pieces of fake plants, just to make it a bit more natural looking.
I have since been advised that using epoxy resin is much more effective for sticking rocks together, and dries more quickly but I've not had a chance to try it out yet.
Anyway, enough rambling - here's step-by-step pictures of the process. Very simple, but effective. :)