I've never had a trap run dry in three months and have generally found them still wet after 6 months. I've never had any problem that way. Spiders, sopugids, scorpions, and such remain quite useable, so long as they are completely in the fluid. I like to use a 2 week interval. But there is often a chance to get traps into a remote area if you can leave them for three of four months.
Black bears can be especially troublesome.
My biggest problem is introduced primates. Especially the male hunting packs that form in the fall. Otherwise the main problem is ground squirrels. Coyotes don't seem to be interested in the trap is covered.