If you're doing it wrong, then Voke/Taunt is the only thing you gonna use.

If you're doing it right as a GLA tank you pretty much cycle through around 15 skills+-2/3, depending on your bars and what skills you got available.

Just a small summary of what I use just for hate.

War Drum
Phalanx 2
Warmonger
Provoke 2
Taunt
Disorient 2
Second Wind 2(using a TP based self heal generates a lot of enmity and since its TP based you will never hav the issue of running out of MP)
Cure 3(in emergencies)
Shield Bash 2
Spinstroke 2

Thats just for hate, for tanking in itself it is...

Aegis Boon 2
Deflection
Outmaneuver+Sentinel
Obsess 2
Rampart 2
Emulate
Tempered Will

It is pretty safe to claim, that if you're tanking serious stuff, that GLA is one of the classes that uses the most skills out of all classes to actually do its job. So it's far from "boring"...