I've hunted the yard around my 1950's vintage house dozens of times. Just when I think I've found everything, out pops another wheat penny or another cool relic. When I really get the itch and don't have time to go anywhere else, I run out to the yard right after work for some fun.
If you have exclusive permission to hunt these places, I would suggest going through and digging everything you detect. Sometimes those pull tabs and nails are masking out other good targets. An example; I have been hunting this old baseball field near my house (city park) at least once a week for most of last summer/fall/ and a few times this year. The ground was an absolute mess of pull tabs, can tabs, bottle caps, clad coins, and garbage. I picked a small section that experiences the most activity behind the dugouts, and dug every target for weeks with no discrimination. A few weeks after I started cleaning out the junk, in an area that I thought had been picked clean, my AT Pro got a weak signal about 8" down. What I found was two 1940s wheat pennies that I had otherwise gone right over several times before. Maybe next time I go, I'll find that silver dime that is lingering deep down there that was once covered by those pull tabs and bottle caps.
That's the attraction of this hobby to me...the thrill of the hunt.