After trying many ways over the years, this is what works best for me and has lasted longest.
First, make sure the head/intake joint is flush and put a dab of RightStuff on that joint.
I fasten neoprene gasket to valve cover (I've used Gaskacinch or RightStuff) and then coat valve cover rail on head/intake with grease, old fashioned brown axle grease.
Torque evenly-cast aluminum valve covers are superior to the stamped steel ones for a flat surface. Also use studs as Barry suggests.
The grease allows instant removal but allows no
oil to leak past. Has worked for me, the motor stays dry.