How can I play effectively with the Guardian?

Blacks Ops 2 has a new scorestreak - "Guardian" which is some kind of microwave turret looking thing. I seem to get them fairly often from care packages, and encounter plenty of enemy deployed ones as well. They seem to be a very different kind of equipment compared to previous offerings, and I don't feel I full understand them. My two main related questions are:

1. How do I use the Guardian effectively? - Where should I put it to make it most useful. What strategies become available once I have one? Normally I just carry it around hording it, and then drop it somewhere haphazardly and it ends up getting killed without seeming to help much.
2. How do I effectively counterattack an opponents Guardian? - Conversely, I have often been owned by opponents Guardians. Is there something to look for or hear to know a Guardian is deployed? Are there any abilities that make it less effective against me, or help me destroy it? What should I do once I'm stuck in it?