Can I install many anti spyware in my computer?

Is it true that one anti Spyware isn't enough to protect your computer from internet spyware?
I have downloaded (I will not name drop one anti spyware) an anti spyware but I still have doubts if is enough for my computer's protection.
Can I install many anti spyware in my computer?
And what would be the best anti spyware for the job?
