If you make your cache tubes out of thick walled ( schedule 40) PVC with a solid cap on on end and a threaded cap on the other you can fill the tube wrap the threads on the cap then screw it down tight you shouldn't have any trouble with leakagee or worry about some critter breeching it. Plus with this type of cache you can use a set of post hole diggers to bury it. I have made several of these in 4", 6", and 8" diameter and they are easy to make the only problem is when you get larger than 6" PVC it get's kinda high. 8" is about $5 a foot here. I made and traded/gave away some at jamboree last fall maybe the guys who got them can tell you how they're working if they've used em yet.

