Siegfried had multiple names from Siegfried/Siggi/Sieg, and all sorts of others which he all understood.

Romulus / Rommy / Rom should both work well.

Actually by a deep and rolling command Romulus can be broadcast loudly well.

I tried to train Sieg with three sorts of command - voice, hand signal and whistle. All three worked to varying degrees with different commands.

When really angry, he really understood, "You f@cking get here right now" and always obeyed that one.

The F word worked the best and he knew he was in trouble if he didn't obey quickly. Not to be used in public places at the top of my voice though.