Just put 4 points into shield skill and get a knightly heater shield, or knightly kite shield (good resistance to crossbow bolt penetration on these shields). Or if you only want to put 3 points into shield skill, the heater shield is pretty good. All 3 are only 1 slot.
I personally don't see any reason to put more than 4 points into shield skill, aside from being able to pickup some of the 5 shield skill shields on the ground that people drop.