We have a guard donkey. Anything moves near the barn he lets loose with that screetching HEEHAW. This sets off the dogs howling.
My grandma used to keep a shot gun near the front door. Anyone who stepped on the front porch was greeted with it.
Get a motion detector light at Lowes for under $20 and install a camera.
Be careful about the gun issue. Check your home owners policy. We have an extra rider on ours incase any one gets hurt on our property- invited or not.
I know I am always mentioning stinging nettle as a deterent,but it really will cause pain for HOURS.Plant some in a pot and you can move it where you need to deter visitors.My ds accidently brushed into some and nothing helped with the pain until I rubbed on some cream we had for denture sore spots.Numbed the arm right up.
This shooting talk reminds me of a product I saw on Worlds dumbest inventions.Forget what the name was,but essentially it was a gun rack for the side of your bed.Lol ,they made it so funny,but it wasn't such a bad idea. http://www.the-backup.com/
My dh hates having dogs,but they are such a good *alarm* system by letting you know when someone is around.My neighbor made the comment the other day that he was suprised that our one dog still goes nuts barking at him.I am thinking *good* that is his job.Neighbors don't always = safe person.