I have a place I've been hitting off and on for 2 years, been there several hundred hours. Just last week I found a Conestoga bell and some old buttons that I missed. The week before that I found a large cent. Now this is a large farm property, but basically most of what I've done is detect around the house and barn repeatedly.
Grid any areas where you find anything, even trash. If you can do so without tearing things up too much, remove all of the top layer of trash. Then detect again to look for what is buried beneath that. This is why I use multiple trips - don't want to cause too much damage all at once. If the owner is amenable to you coming back, definitely do so.