Sometimes I don't want sounds to continue after I hit stop in Mulch.
This is probably a really basic idea, but if you haven't thought of it - you can put a SouthPole in front of whatever contraption (e.g. an Arpeggiator) and configure it so it makes no difference to the sound when the clock is started.
If you set the base gain to -infinity the SouthPole will stop letting sound through when the clock stops.
I've uploaded a patch, I figured it was easier than describing the settings, but the gist is to set the SouthPole with base cutoff all the way up, resonance down, gain down, and then configure Env 1 to turn up the gain continuously while the clock is running.