I MOSTLY do private yards and this is how I handle it.
Before I even start I work something out with the owner. More often than not the property owner keeps anything of value even if they say you can keep some of the things beforehand - seeing the old coins/relics changes their minds. When it comes to old coins, people often seem to believe that they are worth a fortune and they keep them all. I usually just get pictures. The exceptions tend to be properties where the owner doesn't live - rentals or vacant lots. I never feel bad about giving them their own things but I usually do not go back to properties that I spent time on, found nice things and left empty handed. Oddly the people who keep everything usually try to get you to come back and do it again - no thanks
Just be honest and if you don't get to keep the things just chalk it up to experience and understand that you did something nice for somebody else. I know that finding something nice makes you feel like you have some ownership of it, but it just isn't yours. Enjoy the thrill of the hunt.
Sometimes people will say they want a split because of something they saw on TV. This has never worked out in my favor. More often than not there is one really nice thing and a bunch of junk/clad. Every time this has happened, the property owner has kept the nice thing and never gave me half of the value. It's just how things are.
One time there was a man who saw me detecting at my mom's place and he asked if I wanted to do his yard. It was an older house so I readily agreed. He followed me around and I dug a couple dollars in clad and some hot wheels cars. In his back yard I got a V nickel and my first SLQ - it was also my first silver coin ever. He kept the clad and the old coins but gave me the cars. It is still one of my favorite hunts ever and I don't regret that I don't have the coins in my collection.