The growth of calves is greatly determined by genetics. Some guys can train them for years and see only small changes whilst others don't train them much at all and have good development.
As for your lower disc problem when doing standing calf raises. An alternative is to do them in a leg press machine. The flat pin loaded ones seem to work best. Some gyms actually have calf machines and they would be ideal. Seated calf machines (bent leg) work the soleus whilst to hit the gastrocnemius you need to have a straight leg.
Many lifters find they need to work the calves more frequently to see growth.
The Mighty Stu had some interesting things in his thread a while back on calf training. Maybe worth a look.