Caltrops are still bound to Close range and 20 rounds of duration. These can be worked with metamagic, but give the fighter a bow or a tower shield (so he can wait it out) or ranks in Autohypnosis or healing (Martial Study / Combat Vigor / Martial Stance / Draconic Aura) and he couldn't care less about your caltrops
Having a smaller fort than yours because of slightly lower Wis is besides the point. You'll still end up in a stalemate which is a Fighter victory,