I am still recovering from sling surgery 16 days ago. After surgery, my surgen told me he could not position the sling high enough. As a result I guess, I still will leak with a heavy several sneezes of hard caught. Not as bad as before surgery, but not happy with my results. If the sling worked as it should, you should not leak at all after surgery.
As a side note, the surgery area stays raw feeling, and the scrotum stays very tender to the touch. Not sure what method is used to shave the area, but it leaves the area tender and as the hair starts to grow back, you have razor stubble which is also irritating. My leg pain from the position they stretch your legs apart heart for 3 to days and now just if you press on them. I get cramps easy in my upper legs as well now during the healing. I would question your doctor regarding positioning of the sling, any exercise or leg stretching you can do preparing for surgey.