You likely have a fistula, not a fissure (though it can start as such) if you have a seton.
My seton has never caused me accidents. Are you having issues? When I was strictured/narrowed, I COULDN'T go, but now I'm going normally after 3 dilations. I've not had accidents in years, though, and I sleep through the night and have for years, too... So I may be in a different boat than you. Like today, I went 3x, and it's possible I'll go once more before bed.