Hiding Adsense from spiders

Is it at all possible to keep spiders from seeing your Ad$ense code? I've been noticing a trend on all of my de-indexed versus indexed sites and the main factor seems to simply be adsense. That is those sites without @d$ense stay forever, no matter what is or isn't on them.

I dont think adsense would really be the cause of de-indexing your site..since it is a google product and all.

doesnt matter if it is a google product, if they think its a MFA site they will de-index it for quality reasons