I'm confused, what's the issue with a shielder turtling?
They aren't killing.
So, if they aren't killing they aren't a threat.
So, attack a different Target that's threatening.
In any case, the better shielders don't block very often. As they are trying to keep the shield as long as possible for important moments. Such as getting triple teamed by pikes and swords of war.
In that event the shielder gets surrounded anyway due to how slow they are.
Can you provide me an example of a succesful turt,ling shielder, I can only think of two; blocking doorways(kick them, shield break, crush.....three easy solutions) or them running around the flag in siege(stop chasing them, take a step back, and swing so you'll hit them when they turn to squirm about)