I'll have to go and cap that eventually (trying to force myself to run through Vizunah Square today). Even though speccing into Restoration just for that feels like a bit of a waste...
Thankfully since I generally try to set up spirits before actually picking a fight it's not a huge concern, but doing Consulate Docks and getting bombarded was a wee bit annoying :P
As far as preventing interrupts go, your only other choices would be Mantra of Concentration, Mantra of Resolve or to rely on some sort of blocking skill. (Aegis, WoW, Mental Block)
If you're worried about spirits dying too quickly, Armor of Unfeeling might be worth looking into.