Tenant wants to get a pet

Hi folks,

Just after a bit of advice regarding pets in a property. My tenant has been in place for about 5-6 months. The tenancy agreement signed by them stated no pets but they have come to me asking would it be OK if they got a "teacup" dog. My first initial reaction was to say no but I'm trying to balance that with keeping them happy as they have been good tenants to date. However I still need to protect my interests first and foremost ensuring that I'm not out of pocket at the end of the lease for cleaning, repairs etc.

I myself have been considering a number of options which might include some or all of the items below:

• updating the current tenancy with additional clauses to make it clear in no uncertain terms that any damage or cleaning that needs to be carried out is liable to the tenant - however how enforceable is this come the end of the tenancy and they refuse to pay or clear off, I'm out the costs
• getting extra money put down for security in addition to their deposit - again this might not cover costs that could potentially arise
• performing a property inspection before the dog arrives to photograph everything before the pet arrived so at least I have evidence of before and after if required
• nullifying the current tenancy and getting them to sign a new tenancy agreement with suitable clauses as above which would tie them into the property for another year.

Would appreciate anyone's thoughts or advice on this especially if I have overlooked something.

Thanks in advance