There are various exercises I perform to build strong feet. One thing I found to be helpful is combining bodyblade drills with PVC balancing. This will blast your intrinsic feet muscles and will challenge your balance. This can be a fun workout to do with friends. I recommend performing this exercise after you have been working on PVC pipe balancing exercises for a while and you can balance your self for at least a minute. The bodyblade will throw in a whole new element in PVC proprioception training.