J R you base on the amount of risk of a mishap or injury. the bigger or faster or more hazardous the craft the higher the membership rate. someone fly a rubber band powered indoor FF is not going to have the same risk as someone flying a large multi-engine or a turbine craft "this is just an example I know there are craft that fly faster then a turbine or are heavier then a multi-engine craft."
As far as slip and fall accidents you deny claims that do not directly involve aircraft. for the clubs that are leasing land the landowner will not be held responsible for any mishaps that happen on the leased property it is that simple. post a sign that anyone that sets foot on the a club field is responsible for there own safety! the Landowner and the club are not liable for any accidents not envolving R/C aircraft. Enter at you own risk.

Soar Dude