A trespasser is the individual who enters land without the owner's permission. It is interesting to note that you do not have the same duty of care for a trespasser as you would for someone you invite to your home or building.

You may not set a trap to catch a trespasser.

You may use an alarm system to notify the police but you cannot drop a net on the person trespassing. The trespasser does have some rights to not be injured by you.

Do some research if you are hoping to prevent trespassers from entering your property. Posting clearly visible signs, setting up an alarm system or camera system are all readily available deterrents.