I don't have any fetishes Ihaven't shared with my husband but I did have a fantasy that I kept very secret until recently. I unintentionally told him about it while drunk (effing vodka!) and it was the first admission I've ever made that had him less than amused. It hurt his feelings as well as wounding his pride, despite the fact that I told him it was one of those fantasies I would never be brave enough to act out.
I do believe everyone should strive to be open and honest with their partner(s) but only an individual can intuit what their own partner is likely to want to do/be open to doing/freak out over.
If what your mind is cooking up is something you genuinely think he might freak out over, try suggesting other, less intimidating things you don't think he'll mind doing and invite him to make suggestions himself. Spice things up slowly, building on it until you eventually come out with your original desire.
Even then though, you may still find he wigs out like my hubby did (we've been together 16 years and there's nothing much on our 'not ever' list, yet he still hated my fantasy), but as ScarletRose said, if he loves and respects you (and himself) it probably won't be something that'll cause problems. My OH really didn't like my admission but it's water under the bridge already.