I've had animal teleporting turned on in this game, my problem has been with using workers outside my cultural borders, building roads across neutral territory and setting up mines/quarries near cities before the cultural borders expand. I just worry that the AI is going to build defensive units to protect stacks, and plop them on high defense yet camouflaging terrain like a forested hilltop. Is there a way to make a hidden unit come to the defense of friendly units on the same tile when it's attacked? This would solve the problem, and be a pretty cool tactic since you could invite an attack by leaving a weak unit obviously exposed but have a high defense unit hidden in the same tile. Probably would need some combat engine re-work since you would have to be able to change the defending unit after the attacking unit has committed to the attack.