It is not absurd at all. You can't arrest somebody for a sabotage without letting him to execute the deed. Because if he won't execute there's nothing to arrest him for...
So to prevent a sabotage is to have several layers of security (i.e multiple fences) so you will force the saboteur to commit minor crimes like trespassing first and also slow the saboteur significantly so you can arrest him for these minor crimes.
So to prevent a sabotage is to have several layers of security (i.e multiple fences) so you will force the saboteur to commit minor crimes like trespassing first and also slow the saboteur significantly so you can arrest him for these minor crimes.