There are five things that will cause stored bud to lose potency:
1 Loss of trichomes (as pointed out above).
2 Chemical degredation caused by ultra-violet light.
3 Moisture allowing micro-organisms to grow - particularly mould.
4 Oxygen which will over time alter the chemical makup of most organic molecules.
5 Damage/loss by rodents or other pests.
These issues are well-addressed on prepper sites. Briefly you have to protect your bud from all five of the vectors above. Dont allow your stored bud to fall below 0 C or 32F. Keep your stored stash around room temperature in a cupboard or drawer out of the light. I personally use mason jars because my bud does not last long enough for long-term storage
If I wanted to do long-term storage I would use my Andrew James vacuum packer as I do for food.
This will exclude almost all the oxygen from the storage pack.
To make ultra-sure that the vacuum pack does not spoil, I would do what I do for dry food. I include in the packet a small cloth bag into which I put a mixture of fine salt, iron powder (filings might do but you can buy iron powder dirt cheap on ebay) and a touch of ground up vermiculite. Seal the cloth bag with a stapler.
The vermiculite absorbs water and will remove any residual trace of moisture from your bud. It willl share this moisture with the salt. The salt causes the iron powder to rust (on a microscopic scale) causing it to absorb the last traces of oxygen. The cloth bag only needs to be small (about one inch square with less than half a teaspoonful of mix in it for several litres of bud). Pop it in the sealer bag with your bud and then vacuum seal it. Put the sealed pack in a rodent proof container and you are good to go. Packed in this way it will remain in good shape beyond your lifetime.