Hi, I have just adopted a one year old rescue dog that appears to be mostly border collie. When she first came home she was shy and nervous but is now right at home. My husband and I have begun training and she is very smart. she has sit and down learned perfectly already after 2 days. We have begun teaching her to come when called because that is the most important thing we want her to learn. The only problemn is she gets distracted by the littleist things. When she becomes distracted it is nearly impossible to regain her attention. We want to be able to let her run at the dog park with no leash but I am afraid she won't return. How can we fix this problem?