You can also use the Shield as your main weapon, and take one of the Combat Styles (with slayer, as opposed to ranger I think is better unless you can count on a single favored enemy more than 50% of the time).
Shield Slam and Shield Master by 6th... make a spiked shield a great weapon, and now your AC enchants add to hit and damage.
Studied Target also gives a scaling bonus to hit/damage, and a smart fighter should be flanking so you will get sneak attack damage as well.
The Brawler Fighter Archetype gets a slightly higher weapon training with close weapons (shield/spiked shield being in that group).
There is a trait that makes a Heavy Shield a light weapon for TWF purposes.
He also gets bonuses on bull rush/drag/reposition maneuvers, and a lockdown ability at higher levels.
My PFS Dwarf is a Fighter (Brawler)/Slayer, to get Shield Slam without TWF. We kinda refer to him as a pinball machine, with the free bull rush on any shield slam, and if they hit a wall they go prone (no roll, no save). It's really fun.