If they decide to go with polo/golf shirts, I think something small and tasteful on or above a pocket on the left hand side of the shirt would be all that is needed. {I don't wear shirts without a pocket.}
No "tag lines" on the back.
If they go with t-shirts again, I would suggest a contest to decide the best of the best tag line and only use one big one on the back.
I thought the last one was too busy and took too long to read.
Have fun, Phil
P.S. Any further discussion of the shirt should be on the shirt design board.