Resource guarding, techniques to better relationship and trust?

GSD male 14mnth aggressive over food or anything he is possessing. However with vebal command he drops it and its mine for the taking ( not with food ). When I stepped on a paw, I thought I was going to get eaten( I knw other subject ). He listens to every vebal command with a happy attitude. He dosnt stiffen up like this to my four children or my wife, just me ALPHA. We play ball and practice 10x each obedient commands a day. He likes me but not LOVE me, he relys on me but knows he doesnt NEED me. How can I get him to know Im ALPHA but not a bully. He can trust me to have his food and his ball, to do anything I please and know I will never hurt him.