How to defend all my Assassin Dens against the Templar?

In Assassin's Creed Revelations you have to reclaim Templar Towers (like the Borgia Towers from Brotherhood), but this time the Templar try to take them back.

Often I'm at the other side of town when they try to take it back, even worse often they are attacking multiple Dens at the same time. So I'd like to know what an effective way is to defend them.

Should I be using the sewers to quickly move closer or should I simply ignore the attacks and continue with the quests instead?

Keep in mind that you'll only be attacked if your Templar Awareness meter hits max and stays there for a given amount of time. Just kill officials and bribe heralds every time you do something to raise it, and you'll never have to worry about being attacked in the first place.

(One thing to note that's a big difference from previous games - renovating property seems to add about 25% to your meter! It's really easy to max out if you're not careful. Also, liberating a den in the first place seems to max it out every time, but you seem to have a few minutes to lower it before you risk an attack.)

The trick is to have a master assassin (lvl 15 assassin) as Den master. Then the templars can't ever attack it.

So when you have all seven with a master assassin on, you never get any attacks.