Tenant got a big dog

[Mary Jay]

One of the neighbors of my rental notified me that my Sec 8 tenant got a dog that jumps on the fence and ruins the fence. (German Shepard, a young one) 

Lease expires in May. Technically they never asked my permission (on the lease they put they have a cat)

Not sure if they ever asked me about a big dog, honestly I do not think they did...

What would you do?

1) Would you ask them to get rid of the dog?

2) Would you charge them $100 per month extra so hopefully they will get rid of the dog?

3) Do not renew the lease? (Section 8 always pays for them, don't really want to lose them I guess)

4) Tell them to keep the dog inside so it would not ruin the fence? Then the dog will be ruining the house...

Will you guys please let me know what you would do?

Thank you!