OOO OOO I know the answer to this as mine are wiggle butt therapy dogs too. LOL
When greeting, I'd suggest if I think they are being overly exuberant or wagging too hard and especially if it is a fragile client. Just step right over the top so to block the tail. Thus, standing with the back end of the dog between your legs. Tails certainly can be like whips so you need to be extra careful.
Have you decided where you will be visiting yet?
Patch O' luck, and let me know if you have any other questions. I'll gladly help out.
Patch O' Pits Pursuit-O-Perfection
Run Hard at the Rainbow Bridge My Angel Sock-M! I Love You Baby Girl! Now that your Mom Starlit is up there too, please help her learn the ropes, love and keep her company until I can see you both again. Starlit I love you!http://i14.tinypic.com/2a8q345.jpg