Pick up a couple of hunting trail cameras from a hunting store. Walmart has these also. They are used for taking pictures of wildlife in your hunting grounds. They come with a strap on the back for mounting. Disable the flash and place them in equipment or areas that will likely be robbed.
Most of these cameras have an IR, or Infra-Red, light thats not detectable by humans. Even with the flash disabled, you should still get pictures of the perps in darkness. The camera will detect motion and will start taking pictures. You set how many pictures it takes per every motion detection.
The key is how many you use. Place some in the equipment and outside the equipment. They might find one or two but they can't find them all. Some of the better digital ones are $100-$150 a piece. Cheap insurance if you ask me.
The quantity of pictures you takes is also important. If you're not lucky enough to get their faces, pictures of their vehicle and the like can also help. Take all pictures directly to the authorities.
If you know where they are entering the site, place one there as well. Just make sure all the batteries are good. Also, if you are the one placing the cameras, don't tell anyone. If you happen to have someone doing an inside job, they won't know they are there.
Good luck.
