Go full Arms.
You can easily tank mobs with that talent anyway, and it makes your life easier outside dungeons, even if you plan on grouping all the times with friends. As long as everyone is paying attention during dungeons, you cannot wipe, even though a full on prot is a big difference even around level 30, when the finer points start to come to the surface.
I usually use this talent while I level, starting with Arms, then going for the 5 Cruelty, then filling the rest in Prot for better survivability in dungeons till max level.
http://www.wowprovider.com/?talent=1121 ... 502301103iI usually skip the third point in Improved Heroic Strike and only fill it once I need the last point for Mortal Strike, even though at that level it is not really useful (but as a tank, you can still benefit from it).
Seeing the 8 debuff slots, in case you got 3 caster DPS (or anyone who might make use of dots and debuffs) among your friends you will do dungeons with, this might be a better build in order not to steal their effects (only advised if you are really always going to go with at least one more person while questing, because it misses a crucial talent on the Arms tree):
http://www.wowprovider.com/?talent=1121 ... 502301103iIf you are really hell-bent on being a full on tank, then you might want to try out this one:
http://www.wowprovider.com/?talent=1121 ... 502301103iPoints outside the Prot tree can be moved around however you like, I just quickly came up with them. Some points can even be moved on the Prot tree, this is my preference.