As a Gladiator/Paladin once you get Rage of Halone it seems pretty much impossible to lose agro. Shield Lob gives you a good enough agro buffer to easily execute your entire combo, after which you should be MILES ahead on threat. On trash pulls if you're marking things and dps don't go aoe crazy 2 Flashes are enough to secure agro for 2-3 Halone combos.

I have no clue how you can have problems keeping agro as a PLD.