However, it makes little sense to close your gate to keep the stray dogs out of your yard, if they can just come in via your neighbour's gate and climb over the fences.
It makes a lot of sense. Having closed your gate, and discovered a stray dog in your back yard, you can call the animal control people and they stand a good chance of catching that stray dog. However, if you tell all your neighbors to close their gates, the stray is still out there, animal control won't know where to find it, plus you and your neighbors now have to bear the perpetual cost of always keeping your gates closed. There are still many American towns where people don't even have fences around their yards. The difference is that by closing your gate (filtering announcements) you just shift the problem onto somebody else. But if you call the animal control (police) with evidence of wrongdoing, there is a chance to clean up the mess. And finally, history shows that closing your own gates and letting the bad guys run loose, never solves problems, just allows them to escalate. --Michael Dillon