Voadam
Legend
If you want to make legal critters with more defense and not so much increased offense by the rules then advance monsters by monster type HD. Just do not change them enough to change their size. This gives more HD, only a little more BAB, no damage incease and doesn't change CR much.
I would also second the idea of disposable items such as potions of endurance, protection from arrows, or wands of cat's grace for a small hoard. These can boost a monster's defense legally, but can be overdone if every monster is buffed.
Or you can adopt Hackmasters 20 hp kicker, everything (PCs and monsters both) gain an extra 20 hit points so that hacking takes a little longer and low level characters can survive a longer fight (it also means blowing through hoards of little guys is not so easy).
I would also second the idea of disposable items such as potions of endurance, protection from arrows, or wands of cat's grace for a small hoard. These can boost a monster's defense legally, but can be overdone if every monster is buffed.
Or you can adopt Hackmasters 20 hp kicker, everything (PCs and monsters both) gain an extra 20 hit points so that hacking takes a little longer and low level characters can survive a longer fight (it also means blowing through hoards of little guys is not so easy).