How to keep resin from sticking to a mold?!?!

Ok, well Im working on an Omaha beach diorama, and what would Omaha be without the explosions of mortars hitting the water?  I could make them out of plaster or something, and paint it, but I think clear resins and things make much more realistic looking water, atleast for 1/35, so Im using 2 part Epoxy Resin.  I made a few qucik, but nice molds out of tinfoil, to capture the randomness of a plume of water blasting into the sky, as it would from a mortar or a depth charge or something.  So I poured in my resin, and let it sit and harden.  But when it was dry, no matter what I did I just could not get the tinfoil off.  I cut it in half, and It looked perfect, I just couldnt get the tinfoil off!! So my question is what could I use to coat the inside of my "mold" with so that when the resin dried I could pull it out? maybe spray on some sort of gloss or hairspray or something to make a slippery caoting bertween the resin and the mold? or would hose things just mix with the resin?  Also, Im sure you can buy multiple products specifically for this, but Im on a low budget, so are there any other things that would work?

Thanks guys, Ian