The idea of herding sheep (or any other cattle) is quite intreaguing...

Yet I agree, that cattle does not belong into town (for the reasons mentioned above). So maybe there could be an cattle market event outside the town every month(ior week), where one could trade cattle?
Another problem mentioned is, where to leave the flock if you get bored with herding them. I'd suggest just to leave them somewhere on a meadow, guarded by some kind of sheepdog (pet? summon?) which keeps the flock in place and protects it against attackers.
Or maybe go to a farm and leave them there (having paid a small donation to the farmer, of course)...
Shlainn