Savage bitter, with all due respect, you are talking through your arse. My partners and I have always worked on 20% with some very big land owners, and have had good relations with them. You must be a 'blocky' with a small acreage. They are the ones that are the hardest to deal with as they have a different attitude to real farmers.
Experience has taught me that 20% is a reasonable percentage to pay as it works out well for both parties.
I am not talking about hobbyists here, and a hobbyist may get permission on a small block for a box of beer, but professional prospectors are a different matter.
I have large properties that I have worked on where the land owners and I have a mutual respect. They know that there are some who will offer a better deal, but there is no way that these people will honor the deal, where as if I offer 20% that is exactly what they will get. My reputation is most important to me, and that is why I have access to so many properties. My word is my bond.
I have many written references from property owners who have benefited from my prospecting on their land. One local farmer let me detect his property after telling me that a number of people had detected it but found no gold, even though one guy stayed for a few days. After a days detecting I laid out 6 ozs on his kitchen table and invited him to pick out his 20%. He said that I was the first one who had ever found gold on his property. No. I was the first to be honest with him. This is why I have little respect for many who call themselves prospectors. A lot are just greedy mongrels with gold fever.
Offering over 20% causes all sorts of difficulties. If a land owner wants more than 20% I explain to them that the only way I would be interested in paying more than 20% would have to be on a sliding scale. In other words, if I happened upon a large nugget or patch in a given time then we could agree on a larger percentage.
Any agreement should be reached before any prospecting takes place, and a handshake is all I have ever needed. Should a land owner require a written agreement, I see no problem with that as long as both parties are in agreement.
I have imparted a bit of information that I normally would not, but hey, I have more private ground that I have permission to detect than I will live long enough to do so.
My advice is to be honest all the way, as you will want to see an honest face look back at you in the shaving mirror. (unless you are a real dog, and if you are a real dog, your karma will catch up with you).