I haven't had experience, but some of the elements i've heard about are who gets first pick, and percentage split afterwards. Offhand i'd say a greater split should go to the detectorist, while first pick would go to the homeowner.
Perhaps a fair way is to mix the first pic with the percentage method, where someone gets first pick, then depending on the split agreed, the percentage split ensues in turn. e.g. lets say 75%/25% split. 75% person picks 3 items, 25% person picks 1 item, 75% picks 3, 25% picks 1 till it's all gone.
FWIW, the Federation of Independent Detectorists (UK) does a pure 50/50 split based on value from what i've read (but couldn't find it on their site), and they are organized to the point they have liability insurance extended to it's members if something goes horribly wrong, on the order of 5 million pounds, but you have to be in the UK for that policy to be in force.
http://fid.newbury.net/html/fid.htm