Landmines, no. You are not allowed to own them, first off, they are explosive devices regulated by the BATFE.
Secondly, anything that is an undue hazard on your property will cause you to be on the receiving end of a lawsuit if someone hurts them self on it, trespassing or not. I can't even do like the Mexicans do & mortar broken glass onto the top of my block walls. It's a gratuitous hazard.
Simple trespassing is not a reason to use force of any kind, let alone deadly force. To justify the use of a firearm on another person, you must show cause that you had reasonable fear of harm to yourself or another resident of the house, and generally not unless it is IN the house. Kids playing in your yard is NOT a clear and present threat. Laws differ from state to state, but none allow you to snuff another human for simply being on the wrong side of your property line.
Somehow I doubt that this house is your house.. I'm guessing that it belongs to your parents.
I really liked the idea of the motion detector setting off the sprinklers.. I might just rig that one up. Thanks!
Lastly; you really don't sound mature enough to even own a slingshot, let alone a firearm. Please leave those to we who have a clue. Thank you.