From what I have been told once a sling has "healed" into place it is pretty much in place and not going to be moved. Just an opinion from what I learned while investigating.
If you only leak a "few drops" consider yourself lucky. There have been several comments on various threads about the definition of "dry". In most clinical studies and stuff doctors quote they often consider getting down to a pad or so a day to be a definition of dry. I am willing to bet that a very high percentage of sling users and even AUS users will still have "some" leakage particularly with sneezes, coughs, golf swings etc. Many if not most doctors are not totally candid about their definition of dry.
Even with my AUS I still wear a light pad to catch those drops which I think are more from residual drops in the urethera after peeing.