Killing robert guilliman?

[kalous]

I recently found a good bud and we play 40k at least once a week at 1500 pts. He has several armies and for the last two weeks he's been bringing Guilliman along with some wolf calvary and a unit of 5 custodies. They absolutely tear through my 29 genestealers, gaunts and hive tyrants like they're butter. However, I've had luck of trying to 1 round Guilliman by charging him with a Trygon and hoping for good rolls. Is there a better way I could be going about this?

[xenomorph85]

Swarmlord in tyrannocyte, 20 toxin sacs genestealers in trygon is the best assassinate unit combo we have.

Looks like he plays offensively with him, that makes it so much easier to get the stealers in combat with him than backfield Guilleman with lots of screens infront.