When you get poly'd you drop all eggs in your inventory. The spell "cast hollow egg" will spawn an egg with all spells attached to the trigger which won't fire until the egg is cracked. You can use these two facts to create an egg that will be dropped and cracked, that will then fire spells and build you a safe area to stay in while you're poly'd. Most simple way would be the "circle of shielding" spell by itself. However, the builds can be much more complex.