Tastes like poo

When testing the gravity the penultimate test prior to racking @ 1.021 tasted great, but I thought that things needed to go on a little longer. I think that it may have gone on too long! fg 1.005
So a quick question, which is, how to stop fermentation early, i.e when it was at 1.021 (still bubbling like made at that point).
Campden tablets or just rack off?
I will try again with ale yeast and anther with White Labs.
Many thanks.