We knew a policeman who visited my mom in her last couple of years. She had worked with him for years. His suggestion was to put your scariest cacti in areas where someone jumping over a back fence etc. will land in it. So, whether in the ground, or potted, putting them somewhere that people shouldn't enter or skulk is law enforcement proven from their experience.
He also said that it's very effective to have louder, somewhat longer, wind chimes at the right level for someone to walk into at sneaky entrance places that you don't use. Or use every day. Such as one of my mom's sliding glass doors.
Apparently, if people make noise, or get tangled or hurt on something, they more often than not leave.
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