The pole idea works, but only for those places that keep all their trolleys inside the shop. Most of the big supermarkets around here store their trolleys outside, so bang goes that idea.

What they need to to implement electric-fence into the trolleys. Walk off site with it, and BAM! tons of volts through the handles to shock you, and keeps happening every few minutes at random intervals until you take it back

I have been told before that my ideas for 'conditioning' people to do things properly are a bit extreme :P