what brand camera's are you using ?
I normally get several yrs out of mine
next question is, HOW are you transporting them to and from places you install them
as I do know folks that have had issue's with letting then ride in /on atv's and UTV's and the vibrations have beat them up!
next is, whwn you check camera's do you swap SD cards, or reuse the same one over and over!
I have had issue's yrs back with camera's going goofy, after NOT using the same SD card/s , it seems to screw with them for some reason
so, I now keep 2 sd cards for each cam and number them, and ONLY use the same two cards in each camera
been running cams since the late 90's, this has been my experience, but I always get more than a few yrs out of my camera's now!
I even have some super cheap Tasco's (25 bucks each) that are going on a second yr running 24 7
and still working great! easy 25,000 pic's off the one so far too !