I have truesighted many times and thought I could take them easy. Then I try to attack and protection...One evening I tried 4 or 5 targets before I found one not in protection.
I will admit, I am not a big fan of unlimited check protection as some players will just go check player after player and share who is open to their province or ally list.
On the other hand, I do find it frustrating to cast truesight, then try to attack and they are in protection... Wasted wizards many times.
How about rather than a check protection at the attack stage, when you go to cast a truesight, it checks and you just can't cast truesight unless they are out of protection. Just make it like the attack and protection, instead of a magic success or fail, you get they are in protection message. and the wizards don't get used.
Just a thought to avoid wasting wizards on someone that you cannot attack.