http://fallout.wikia.com/wiki/Stonewall
Ah, it's supposedly bugged in the same way as Hit the Deck, gives it's buff when you're USING the type of weapon it should be protecting from rather than AGAINST it. Although, looking at the perks in the GECK, either they got fixed and the wiki never got updated or the "Modify Damage Threshold (defender)" entry point is bugged, which can't be fixed very easily and which also means any perk that uses it is broken. Gonna test in game real quick
EDIT: Ok, some definite weirdness going on. Through some quick testing, before taking the perk, a lead pipe armed, max-special max-melee NPC was hitting me for about 25-26 damage consistently. Afterwards, equipping a melee weapon caused an APPARENT increase in my DT on the Pip-boy, while I was taking around 20 OR all damage negated* by armor from the same pipe-wielding enemy. However, I wasn't paying much attention to the type of attacks used or any damage completely negated from before the perk, so those spikes may have been from power attacks. Letting him attack me while I wielded a melee weapon confirmed that it was power attacks that were getting through, and still being around 20. So it seems the perks work right, but the displayed DT is incorrectly calculated
*One of the mods I use gets rid of the 20% damage that is always taken regardless of DT