The Dink Network

Sounds like you've already lost this battle, try playing offensively and take the fight to the Orks next time? Go for the kill on one tribe (or at least constantly harass both of them) while expanding as aggressively as you can as early as you can. Such a strat usually works in most situations if you're going up against the AI. If you're playing a campaign stronghold mission, just go get more honor guard units.