I disagree with the leg 'tap' to get his attention.
attention or focus isn't easy especially with a young dog & such fun distractions.
work on getting/keeping his focus at home, which I think you have already, right? but work some more.
use a toy or treat & the key words like 'watch-it' & have him follow your hand in small steps, close to him then further away until your hand/toy/treat is right between your eyes.
make sure he learns/responds well at each step before you go on. make this a fun fun fun exercise & realize that his attention span won't be for that long at first. you've got to gradually increase the time.
you might also work on 'settle' as in when you are playing/whatever & he is rowdy, say 'settle' in a slow calm drawl, ignore him by turning away, watch out of the corner of your eye & when he settles even for a split second, then he gets calm praise/treat.
then you continue playing.
**gradually** increase the amount of time you expect him to watch-it or settle.
its hard with a really smart dog - but you've got to be on step ahead to make it really interesting for him.
all of this can be done without even having a collar on him. dogs really get into the habit of pulling against that resistance & that creates more problems.
have you considered a 'gentle-leader' its like a horse's bridle.
you might also, if possible, try to wear him out a bit playing before you encounter the other dogs.