OK, let me start with a picture, then onto the question...



In the above picture, what I'm trying to do is set the infantry so that the tanks behind them can't be charged. the troops have a little under 1" each other. (Ignore the LRs in the back for now, they'll have their own screen) Now the question for the rules lawyers out there: Can the tanks be charged? It almost seems that as long as my opponent can get a model between and 2 guardsmen then he can charge them, so do I need to have them even closer together?
My tanks are always getting killed in HtH by "not cheesy" Blood Angel assault squads and I'm hoping he drops a veteran assault squad w/Dante right in front of them and find that he can't charge the tanks, charges (and wipes) the "screen", then gets plasma'd to death.
If this doesn't work (by rules), then how many infantry does it take for a successful "screen"?