I am unsure why this happens but it is upsetting me so much. When we go walking I let the two of my Labradors off the lead and then thats it, they sniff for a while and then are charging at each other knocking each other over biting each others neck making aggressive sounds and up on their back legs ... has anyone any idea how to deal with this behaviour? is it just a phase?

The youngest is just over a year, male, golden and the other is nearly 2, female, chocolate - they love one another, and are so good at home. What can I do? They SO don't listen when I repeatedly raise my voice and tell them 'No'.

Could anyone recommend anything?