@layman,
I would not, however, be as concerned about establishing and requiring some space between hostile "counter-protesters" and an assembly of peaceful protesters.
If they want to protest, and can't restrain themselves from disturbing the peace, then let them get their own permit, and hold their own "rally" elsewhere.
There was a similar protest in Charlottesville last month. It was reported that there were about 50 protesters there, surrounded by over 1,000 so-called "counter-protesters," whose only real mission was to get up in the faces of the protesters, scream obscenities at them, and completely drown them out, thereby effectively depriving them of their right to speak via a "heckler's veto." This should not be allowed.