Last year was our first year with our boat and I had the same concern trying to make it easier for my wife and family to hang fenders. I chose these from Seadog ( Manuf. # 327200-1 ) available at west marine. The product photo on west marines site shows them connected to the pulpit but there is an insert for connecting to life lines.
All you do is open the lever, place on life line, pull cord to adjust height of fender and close lever. Never had an issue using them, and the easy height adjustment was great for setting different heights for docks or rafting up.