Deep Wounds will help you quite a bit with threat. I see little point in grabbing Impale but neglecting to grab Deep Wounds.
You also should reglyph. I would run with Devastate and Shield Wall glyphs at all times (make sure to grab the Improved Disciplines talent, to make Shield Wall a 40% cooldown every 2 minutes - very handy), and then swap out the third glyph depending on the fight. Last Stand, Taunt, Cleaving, Blocking, Vigilance - there are a lot of viable options, get a scribe to make you several stacks of glyphs and just play with them for different fights. (glyphs are very cheap if you have a scribe friend)
Thank you very much. My expertise is very low but my hit has gone up. Should I be gemming to get more expertise?
No. Gem stamina except for one purple gem to match a high stam bonus so that you can activate your meta. Tank threat is mostly dependent on your rotation and spec than stats. That said, if you have the pieces to get to 26 expertise with the food buff it is helpful by removing dodges, but not game breaking. I tanked most of ICC with 16 with no issues.