try AFTER upgrading he′s brain.
I assume that only Lupa's brain would have prevented such - and I don't see that being as huge an impact as one might be lead to believe. I have multiple issues with rex
1. Super high perception - this causes him to run off after enemies
2. Attack is a bite - after running to said enemies he is shot multiple time while trying to close in
3. Cyber dog frame - I think it looks terrible (I suppose this isn't really a legit complaint)
4. No dialogue (suppose some like this aspect)
All in all, the only reason Dogmeat was serviceable in FO3 was beacuse he was glitched to be invincible. I just don't think a dog has much use in New Vegas. Just my opinon though, I'm sure some people love him.