Well there is a few things to keep in mind: DnD is an AoE damage boost. Heroic Strike is single target. DK'S are alts of 80's and usually come with attitude.
If you ask someone not to do something and they keep doing it, let them die. If they kick you from the group, you can cue again right away instead of waiting 15 minutes for the deserter buff.
Check out Aggathon's prot warrior guide for specs/glyph choices and work off of that. It should give you the best threat possible at your level with appropriate gear. Really, I'd just try to work harder at holding aggro.