We played a game a while back, I was the last remaining Xeno player, and it took the enemy 3 rounds of concetrated fire/assault power to get through me, and this is why.
Dredd mob, with 12 Killa kans, surrounding 4 Deff dreads, middle one had the force field, flanked on each side by a Kustom Stompa both of which carried a Big mek with
KFF inside. My army was around 3500 points but i took out of 9000 myself, thanks to no titans, my biggest threats were baneblades, which my stompas tore apart. The KK destroyed the infantry while the Deff dreads ripped apart anyone gewtting close. The entire group had a 4+ cover save, it was a beautiful thing. Next time, i want to run 4 Stompas with Big meks with force fields surrounded by killa kans and one Big dread to have a forcefield, so they can spread out a bit more. Everyone saw me placing them and thought, eh, they are just walkers, they can be destroyed easily enough. Unlike the shields on titans and such, mine cant be destroyed, my 4+ cover save is absolute

I urge you other ork players to try this out, I had so much fun, laughing as lascannons and such were almost useless, the stompas blocked a ton of
LOS drawing fire <plus those too scared to shoot the Kans> I captured my starting table by turn 2, and even made it about 3 feet into the center table, at turn 5, but by then i was all alone, hehe