"OK that answers my question. But how are you guys getting hooked up with these? Do you guys just ask the construction crew?"
Several ways. If the demo crew is there we ask permission. Many of the sites have been bought by home builders and there are signs on the lot advertising. We ask them for permission and in almost every instance they have no issue with our being there. On public land we just try to hit them on Sundays as a lot of the projects, streets, sidewalks, etc., are busy on every day except Sunday. Sometimes the construction crews will permit it but I have been asked to leave a few times also, as the 'liability' question comes up. On most demo sites, we just show up and detect them unless there is "No trespassing", "Posted", "Keep out" or similar sign up. We have NEVER been asked to leave and in many instances were invited to other sites.
If you live in a large city, check the web for a site that lists "city demolition permits" , then go from there. We copy the list, drop it in a spreadsheet, check the tax records for owner and date house was built, then map it to Microsoft Streets and Trips, then print maps, then establish GPS routes to hit them in a sequence. It has really worked well for us. We usually are on site at around 7:15 or so and quit at noon, but with cooler weather we might start at a later hours and quit later. In the last two months, September and October, Mark and I got over 80 silvers and over 500 wheats, not to mention the several hundred other coins, jewlery, foreign coins, tokens and toy cars.