The Trijicon RMR is already very durable but if you are looking for even more protection, check out the new RMR-G (RMR-Guard) from Weapons Armament Research. This drop-in part is designed to protect the glass from smudging during palm charging and protect the RMR itself from damage when charging against hard objects like walls or tables. It will be available in two versions – one that is just a guard and one with a built in rear sight.
Pre-orders should be open soon. WeaponsArmamentResearch.com