My dad is a plumber and has one of those piping roof racks on his van
For those that dont know. Now someone has opened it a few times and tried to take the pipe from within, its not very often theres any in there but its very annoying to find it has been opened!
Now my dad isnt overally bothered as its empty 99% of time but I on the other hand want to catch them!
What can I do, im thinking something to put on it or when they open it. Anti vandal paint is an idea or something inside that pops out?
Got to be easy to do so nothing to clever.

For those that dont know. Now someone has opened it a few times and tried to take the pipe from within, its not very often theres any in there but its very annoying to find it has been opened!
Now my dad isnt overally bothered as its empty 99% of time but I on the other hand want to catch them!
What can I do, im thinking something to put on it or when they open it. Anti vandal paint is an idea or something inside that pops out?
Got to be easy to do so nothing to clever.