Mental ? A myth – highly intelligent and if not channelled then they get bored and can become unruly and disruptive and hyper – I suppose like any dog that was bred to work and then not living a full and challenging life.
I have had the pleasure of being owned by 3 in my life (so far) All different with different personalities and different needs. Not one of them “mental” but all well trained and well cared for and exercised both mentally and physically. Nacho is the most wonderful creature I have ever encountered in my life and that includes the two legged variety. ;D