Kane is right...
A frequent mistake when deadlifting is slightly flexing the elbows. That is a good recipe of bicep pulls. But if you avoid doing that it would be difficult. Over-under is perfectly fine. But pronated (over-over) would be a better grip trainer if used for you overall grip except for when you HAVE to use over-under.
Definitely no mixed grip on rows! Tell the guy who says "always use straps" to stop being a wimp