How can I catch trespassers?

If you have some money to spend you could use a game trail camera. Good ones will snap a picture of the trespassers and show the date and time the photo was taken.

Made for rugged areas (hunting grounds) these are durable cameras that take a shot any time something moves into the frame.

It will not injure the suspects, but if you are looking for evidence that certain people are trespassing on your land ... what could be better than a picture?

Use a nature camera used for hunting. U can put it out there and it will automatically take a picture of them when they walk in front of it so put it where you think they always go. And then if you have them on camera and they are vandalizing you can bust them. the cops should listen since you have the proof of who did it. If that doesnt work, then depending on where you live you can use bear traps if u really dont care about hurting them or breaking the law.... lol. but a dog would work too although in some places they make you put that dog to sleep if it really hurts someone bad enough to make them report it. even if they were trespassing and it happened on your property they can still kill ur dog because of the attack

Motion activated cameras and/or lights tend to help. There is really nothing the police CAN do if the perpetrators are not caught in the act or on video. Unless they leave identifying evidence behind, it is nearly impossible to track them down. Just because you 'know' how it is, that isn't EVIDENCE.

Video surveillance, or just borrow a friends pit bull for a few days.

leave your front doorr open wait for them to come in and pop both there heads