Pick an exercise and what you want to do is get a total of 75 reps.
But pick a weight that you can barely get 20reps. After you do 20reps give or take a few, shake your calfs out for no more then 5-10 seconds and then keep hitting it til failure. All the same weight through out. Once you get up to the 60 rep mark the weight will be extremely heavy and you will only get a few reps each set. You will want to rest more but don't that is the point. Try this twice a week changing up the exercises each time. If you want to go more then 75 total reps then so be it. Always keep your feet straight ahead and concentrate on pushing off your big toe for some sets and your middle toes on others.
Give this a try when you want to change things up once and awhile. peace