I feel for you. I had that happen once and would never let it happen again , the time involved in the history search ,the hours of digging, before i start any of my permissions, i let them know i am a History, Relic collector and the finds i will keep or i will move on, i have a permission and find form that we both go over so there is no legal part left out, unless they are Family pieces or worth millions were legal agreements will take place . I have now 136 sites and all the land owners are just awesome and understand, and i have found items in the 500.00 to 1000.00 dollar range and all have granted them to me cause they have seen how hard of a hobby it is by just watching, day after day and i do show them all my finds.