This is yet another government-created problem.
Firstly, they prevent landlords from taking a larger security deposit to cover the risk of uncovered damage.
Then, they make it very difficult to claim from the security deposit.
So, don’t blame the landlord who looks after his investment - he doesn’t know you or your dog!
We have one flat where pets ae not allowed by the Freeholder, so we have a good get-out clause. 
If they were allowed, I would be prepared to consider a small pet, depending on the tenants., but I would wish to interview T’s first before agreeing.
I’m with you on that Collin
Been LL for 30+ years. The truth is that I can’t recommend my children to take on the houses and continuing to rent. They’ll all get sold.
We take pets but they pay £10 PCM for their own personal space in the house.
FACT - pets reck houses. You never get the cost back. There are benefits, the house I’m improving was rented for 22yrs. Then it’ll get rented to a family without pets but they’ll often do it without our knowledge and giving notice to someone who illegally got a pet. Pipe dream.
Good tenants are like gold dust.