I use it on my provoke macro. Something like

/ac "Provoke" <t>
/ac "Shield Lob/Tomahawk" <t>
/ac "Cover" <tt>

Basically I'll target the loose monster and mash this macro for a bit if I see it suddenly gun for someone else for whatever reason. By mashing the macro, I would first provoke and then use lob/tomahawk as soon as my gcd is available. I use lob/hawk because when I lose threat on this mob, it is unlikely that I am currently targeting it, plus, I found that the enemy enmity list (the colored symbols) to be slower on the uptake than the actual enmity bars on the party list, so it is also likely that the monster has moved out of my standing position. Lobbing my shield at this point will likely break my combo but it hasn't screwed me over so far.

Anyway, at this point, if provoke and lob combo have not brought back the monster to me, the monster will still be targeting someone else (like healer still adamant on overhealing, for example), at which point the macro mash will make cover <tt> kick in. When I see that cover icon come up, that's signal for me to move over personally and wrestle it off the party member. If mashing this macro over one gcd does not make cover pop up on my scrolling combat text, that means I have regained aggro smoothly and the monster is targeting me (cover wont kick in since <tt> will be directed at me, can't really cover myself huh) so I'll let it come back over and pile a little bit more enmity on it before proceeding normally.