Good advice by Val there Brisad. 99.9% of the the items we find whether coins or artefacts have been lost spread or thrown-away and this can and does happen anywhere. These actions don't generally happen on a habitation site, so you may find a Romano British settlement but you'll find very little "on" it, though 100 meters away may have been where the midden was or the fields where they spent there time working and that is where the finds would be.

Granted there are areas of land such as pre-wooded or reclaimed flood plain where the footfall through history will be far less and therefore the chance of potential losses is that much lower.

Nearly every field will produce something be it only modern and you can do as much research as you like to increase the odds of finding that special something but at the end of the day if you know your machine then it's a numbers game, the more yards or even miles you cover the greater the chances of finding