Could always put a bounty on the strays once the invasion is stopped.
well they might have enough fear in them to straighten up and stop causing problems too. So the problem could end. As long as we continue to have grafitti removal programs and keep covering up their crimes, we are willing to just tolerate their juvenile criminal behavior.
The minute we stand up as the great giant country we are and say we have no tolerance for this crap, we will first see how big the problem really is, then we deal with it, it will shrink immensely.