cooks 7

I need to move a couple things around on my exhaust for some ground clearance, the one major change I need to do is to move my v band joints from where they are now under the car upstream towards my headers, my problem is this, if i do that, my vband joints will come before my o2 sensors. I have a friend who is a mechanic that says any oxygen leaks around the o2 sensor will throw it off badly. I figure that on most setups the manifolds have a joint to the rest of the exhaust before the o2, anybody have problems regarding leaking exhaust and faulty readings? I realize my vbands shouldn't leak, i am not sure if they do or not, if there is a small leak will that give me problems? When i was talking with him about this, he was mostly referring to people who run their o2's too close to the end of their exhaust, like when running open headers at the track...
If anybody in the tuning arena could chime in, that would be great.
Thanks
Jon