Haha insane man! What's your setup? Don't even think i have reached 51...
i dont remember, i think it was a few totems of healing near the castle, i then placed 4 totems of firerate, one 2 tiles on the right, one 2 tiles on the top, one 2 tiles on the bottom, one 2 tiles on the left, and place arrow towers in the outline of an 2x2 area around the castle, put spikes around the thing (atleast put some, all will be expensive) and put some houses/earning totems and other cheap things anywhere to act like shields, i explained it badly and i should have screenshotted it