My neighbour and I walk our 3 border collies most mornings in a very large urban park.
One of these dogs is a five year-old dog that is not neutered. His name

is Fyles. They bought him when he was about eight weeks old and to their knowledge, he did not have any traumatic experiences at any time.

Fyles has always been skittish around bicycles, young children and skateboards. When he is walked on his leash after school is out, he usually pulls on his leash and wants to return home. There are no young

children in his household.
The real problems occur when we walk the dogs off-leash in the large park mentioned above. Fyles' ears go back and his tail goes down when he sees a bicycle. Prior to a couple of weeks ago he usually ran just off the path into the tall grass or a few yards up the ravine. A couple of times he ran up the ravine and out of sight. Sometimes he found us after about 15 minutes and once we called him and searched for

about an hour. However, we also saw what he was running from. In the last couple of weeks he is running away and out of sight several

times a day. Sometimes we see a bicycle. Other times there is another person walking a dog about 30 yards away. On some occasions we cannot see anything. He runs up the ravine and out of sight and he disappears for anywhere from 5 minutes to half an hour.
Any and all suggestions are appreciated.
in thread "(Email Removed)" (Email Removed) whittled the following words:
My neighbour and I walk our 3 border collies most mornings in a very large urban park. One of these ... of sight and he disappears for anywhere from 5 minutes to half an hour. Any and all suggestions are appreciated.

If a dog is NOT reliable off leash, they should not be allowed offleash.Period.
Obedience training, and a reliable recall. You can't expect the dog to stay around without training. It could be many things that make it bolt on you. But with training, hopefully you can get the dog's obedience training to be it's natural reaction when it wants to run.