I had intended only to lurk today, but found your post and felt the "need" to reply. I too suffer from this problem. I had the bladder surgery with the new sling and two months after, I heard the POP and then immediately released urine. It's been a real problem ever since....especially during the pneumonia I have just been getting over. I had to go back to wearing the undergarments (especially at night) too. and even in the daytime for several days. I always have to have some protection!
For a while after my TLIF L5-S1, I had pretty serious fecal incontinentance too and that was a real problem. I think the nerves have healed somewhat and that problem has mostly resolved itself, but the urinary problem is still there.
I went to a Uro-gynecologist a while back and even went to the pre-op apt to have the problem fixed...but, he gave me a 50/50 chance of improvement (or further damage) and that was simply not good enough! So now I live with it. Naturally, the first Dr to do the bladder surgery caused enough additional damage to have a new cystacyle and rectocyle (please excuse spelling). When it becomes impossible to do otherwise, I will have complete pelvic reconstructive surgery done.
I wish you all the best on this!! I hope you find some relief!