There's really two classes of mitigation cooldowns that all tanks have access to: rotational cooldowns (decent effect, >10s duration, shorter cooldown, like Rampart, Foresight, Bulwark/Awareness, etc.), and tankbuster cooldowns (powerful effect, 10s or less duration, longer cooldown, like Hallowed Ground, Sentinel, DA-DM, Living Dead, Holmgang, etc.). The tankbuster cooldowns are the ones you should be saving, if anything, because they are the ones that can actually save you if the shit hits the fan. The rotational cooldowns are substantially less effective, and are more designed for smoothing out incoming white damage; they cannot and will not save you in a pinch. You absolutely need to break the mentality of "cooldowns are for saving my ass" and realize that that's not how tanking works in this game. The amount of damage you mitigate passive through your tank stance and through the gear you wear is a pittance compared to what you can provide by keeping up at least one rotational cooldown at a time. Especially when there are so many of them that last for so long, there is absolutely no good reason why you should not be rotating them.