So, whilst playing Dead Money for the first time, I realised, after Rescuing Dog/God then Dean, that I could only have one companion and would have to leave Dean behind. So I saught to protect him. I put down a small minefield of Frag Mines and Gas Bombs. All went well after returning from Puesta del Sol whilst exploring. Eventually, I rescued Christine, and told her to go back to the fountain. I followed her along the way, but stopped to fight Ghost People. And lo and behold, when I entered the Villa, my collar exploded. Instantly. I reloaded, and realised I was trapped in a loop of my collar exploding. I thought it might be a restricted area, but realised that, after toggling God Mode, all my companions except for Dog, who was with me, were hostile. I tracked this back to the fountain after a few StopCombats, and realised that as Christine was passing my mines, they exploded and she turned hostile. One more StopCombat, and all of my companions were crippled, and I was rather annoyed. Not only does this break my immersion, it also annoyed me.
So that is my cautionary tale. Your companions are better left unprotected!