"Sheep swallop. Sheep swallop and bloody buttered onions."
Though in general, I just say the fucking word. Be it frak, feck, fook, or fuck... the meaning is the same, and it should be treated the same. As in not a big deal. Cover your child's ears all you want, they're going to hear the word, and the more you tell them not to say it, the more they'll say it when you're not around. Taboos don't work.
There is a time and a place, though... when I know I'm around the easily offended, I'll either offend them and not give a flying fuck, or I'll do what I did as a soldier, which is say absolutely nothing that isn't absolutely professionally necessary... in the coldest, most inhuman tone I can manage. Waaaaaay worse than cursing. I've disturbed many people with that one.