I live right next to a bike path and bikes come by my house everyday. Whenever he sees a bike, he barks and lunges at the bike. I need to find a way to stop this.
Is he a herding dog? Some dogs just have it in their blood to chase things. If you really have time, sit in the park and when someone goes by, distract him and don't let him bark. When the biker goes by and he doesn't bark, praise him and give him treats. Repeat over and over till he gets the hint that he shouldn't bark.