Their weakness is in their pathing. It is better to lead them around inside the black forest where they will have to go around trees and rocks that you can fit between. They also walk the long way around fallen logs, and can't jump up steep inclines. By running back to the wide open meadows you made it easier for them to follow you. Stay in the black forest and slow them down on the terrain, then you can get far enough away for them to lose interest. If it's a log troll, they will knock trees down for you and create their own obstacles.