Can I have 2 installed anti-virus on my system, one running scans only & the other running scans continually?

I have AVG anti-virus on my system as primary anti-virus. I also have Clam-antivirus on a program called Spyware Terminator. I can enable it to run scans, and I can also enable it to run as realtime Shield. I wanted to enable the anti-virus without the shield, but I want to know if that's safe too...