I don't see tarpitting it working, what with the stomp attacks and all. And it's going to take a lot of shots to kill it, but on its own, it can only do so much damage. I think ignoring it is probably the best strategy. I think the problem will arise when people bring three or more to a fight. One can be killed or ignored, but three knights moving 12" a turn and shooting their way up the board will not be easily dealt with. Unless you have a ton of melta or a few flyers, but then we get into the all comers list argument, three flyers or three drop pods full of melta sternguard is hardly all comers.