I wouldn't bother trying to find anything they don't like, even if they don't like it they will try and eat it over and over and over again. Are you planning on letting them free range around the planter and eat whatever you plant straight from the planter? If yes, they will just eat everything, rip the roots out and things will never have a chance to grow back with them always in there. My goats get into everything all the time and wreck everything. I love them anyway but man sometimes....... I have five and they drive me up the wall daily!! Good luck though!!! If they aren't eating the garden they are "prancing"(crushing), "frolicking"(pulverizing), and "lounging"(laying flat out on top off) your garden!! Veggies that my goats love are turnips, corn husks and all, carrots, kale, swiss chard, and parsley, but by far they love weeds!! Weeds of all kinds, thistle, dandielions, clover, and even young stinging nettle!
Meg