While I don't have experience with a lab, I do have a little bit of experience with some males. If you're not sure how he's going to be, I'd recommend putting some socks on his paws if he'll let you. If not it should be fine, might get a few scrapes. As for the knot, it may take some tries but I'd recommend going for a pseudo tie, either her reaching back or you if you're present to carefully hold onto the knot to avoid it from going in but still giving that feeling of a tie. That way if he gets excited, he can 'pull out' without harm and you two can gauge his excitement without much worry.
I'm not an expert, just things I missed out on when being with a male shepherd mix of some kind.
