How to catch small bullheads in a pond while bluegill fishing?

in this pond , theres alot of bullheads that get up to 8 inches and me and my dad only get very lucky to catch one while bluegill fishing, so i would like to ask, how to catch bullheads that are small , not big because they dont really taste good as the small ones. ...i also want to kno what does shallow water means... i never got wut dat really meanz... thankz :)