After reading the comments, part of me wonders how long before someone does some stupid copy cat **** that gets them arrested. Bear spray?! ACID?! Outside really IS bad.
"I got sued out of my house because I made a package thief trap with <insert dumbass idea here>."
Glitter was (and still is) an excellent choice. Much more diabolical--even one of the 'victims' of the trap mentioned what his gf would say about all the glitter.