If your rook is Hammer Slam built, save your slam for after bite, preferably saving it for when he's got 2100 health (assuming maxed slam and roll, adjust as needed). Most Erubi will try to get you to waste your nukes, and then bite. By refusing to nuke, you cause him to use his heal prematurely, which means he'll have difficulty recovering from your massive nukage. Of course, if he's good he'll just batswarm away at low health. Beware the Erebus player as a slam rook.
If you're a tower rook, you're in luck! Hide in your farm, let him fight you for a bit, and roll him as he gets to low health (you have to watch your opponent and ascertain about how far he's willing to go before he batswarms, typically a player has a certain amount of health that he or she simply deems an unacceptable risk. This is where you roll them.
UB just needs spit to ruin HoL. Spit on him when he's gonna start running, and he'll probably mist to get it off. This essentially stuns him for a few seconds, giving you ample time to catch up. Yay! Proceed to eat a delicious Erebus meal. If he doesn't mist out, well then at least you got the lane to yourself. Spit him again if he's low enough.