Pets being vulnerable hasn't been balanced since day 1, since they take damage similar to what mobs take. There is no gameplay in preventing possible grief--a couple Flamestrikes is all it takes. (Original UO didn't have such high PvM damage, apparently, so it wasn't an issue.)
So, either have them instantly bound upon successful taming or do something about their damage taken while they're vulnerable.
So, either have them instantly bound upon successful taming or do something about their damage taken while they're vulnerable.