Hi Alistair,
Welcome to the class!
Is not the current cleat as quick release as you may need? (if you leave the tail out of the secondary rear 'tidy up' cleat.)
I similarly sail at a river/estuary type location and if I know I am cutting a corner or avoiding tide through shallow water I will lean back and uncleat it in case it touches.
If you tighten the rudder stock bolt an extra little bit the rudder will stay down quite well uncleated provided you are not going very fast.