I agree with preacherman, using GPS is a good way to not find it if you need it.
I would reccomend using the pvc meathod, although ammo cans work well if you double wrap them in plastic first.
break the rifle down so it fits
wipe it down with transmission fluid
Its a good idea to wrap the component pieces of the rifle in plastic bags or vacume seal it, make sure that most of the air is removed and there is some liquid transmission fluid in with the parts.
(don't burry anything with a scope obviously)
make sure trans fluid gets on every surface. Trans fluid does a darn good job of displacing any water that may get in.
one thing to remember is to put a block of wood in the bottom of the tube so that if water does get in, it won't pool anywhere where it will be in contact with the rifle.
The double tube meathod of burying works well, however the single tube meathod will work if you attach nylon strapping to the body tube with stainless hose clamps.
the last thing you pack in the tube should be a package of clean rags and a towel to lay parts out on with a dissassembled cleaning kit, double wrap it in plastic, put a desicate in it (get em from a shoe store, every pair of shoes has a little bag of it in the box)
Either way you do it, don't forgert to put a really really strong handle on the container, preferably attached to the bottom of it, as wet earth has a tendancy to develop a wicked vaccume if your trying to pull it out.
If you have the option of securly attaching a long nylon towing strap to the container, you can burry the strap end just a little bit under the surface and use your truck or car to pull it out in a hurry. (sometimes you don't have time to dig)
For ammunition, the same container with a block in the bottom will work, if you are packing loose rounds, its best if you use mil surp as the primers are typically waterproof and the powder can handle sitting a long time. make sure not to get corrosive ammo as you may not have an opportunity to clean your rifle propperly.
If you can get the sealed spam cans of ammo great, if you have lose rounds, place two or three trashbags inside the container, then fill loose ammo, its best to leave a little space at the top as it makes it easyer to close the container. A light coating of trans fluid on the ammo keeps it functional and non corroded, don't get carried away, a cup or so is max.
seal each of the layers of plastic independantly, making sure to get all of the air out, then seal up the container in the same manner as before.
roll or rotate the container to make sure that the ammo is evenly coated with fluid.
One thing to remember if you are using the pvc meathod of stashing is it is rediculously hard to get pvc apart with your bare hands if you are in a rush.
I'm probably forgetting a bunch of things, but I think thats the main stuff to remember.
