I know it causes agression I know over 50 dogs that had got agressive on a chain! I told her this. she told me that roxy would never be agressive and then i stopped there!! I have a neighbor that has a beutiful choclate lab and is kept on a leash and is agressive!!!! My dad has gotten in a big fight with the owner about that!!! WE know that it is causes agression my baby eneded up in the vet over ngiht because the lab attacked, we finally turned the dog in after that.