Their prayers cannot protect them in any way, but they aura can do that. Every person has an aura and, if you curse a person who is stronger than you, that person is protected. It may happen there are some lost Souls, who may be Satanic or were with Satan, who do not find the Truth in this life - so they may be naturally protected in a way, while being under xian programs.
I always talk by experience, as it's the most reliable source for me instead of talking, and I have met some exceptions.
The enemy has power and energy (every day less), and I met some very weird and negative people who were clearly under the eney protection, even if they were not jews. Shabbos-goyim I think, servant to the jews, who enjoy protection for being useful to the enemy.
Anyway for standard xians, it does not seem their prayer can shield them in any way, to me. Just their aura, in case.