Mom has a shock collar that she uses with the dog at times.
Just put the collar on, and it is amazing how well he behaves.
And the simple beep is apparently very good at catching his attention.
But, it sounds like you've only been doing this for a shot time. You'll have to get your feel for it long-term. Also it may depend on whether you're always riding on the flats, or if you are pushing 20+ mph on the hills.