Also mint is a fairly good deterrent. Alternate the Irish spring and some bags of mint tea to prevent them getting acclimated to one smell. There are also some flashing LEDs that people put under campers to prevent mice/rats. Apparently they can suffer night blindness after a bright flash just...
it is more about CFM than tank size. I have a 20 gal husky that is kind of disappointing. It pretty much runs non stop because the compressor is so slow. I have a small harbor freight sand blaster that i would give you. You just need an air compressor to run it.
As far as motives are concerned it is anyones guess. If they are not putting up warning signs explaining intent I would discount this being done to be helpful.
I don’t think it is legal to modify trails like this without approval. (Read paying money to tha man)