It is public prop. But lets keep in mind, some home owners take great care of the lawn that may be there as they do in their front yard. Put yourself in their place, and think about how you might feel if looking out your window you see someone out front digging into the strip that you have taken care of. I am NOT saying that you can't, I am only saying that, as in anywhere else detecting, good judgement and common sense. I have found a few good things in those strips, but it's always been in front of vacant or abandoned houses etc. It's always a judgement call.