Tenant wants to bring foster dog home

[Bienes Raices]

The tenant wants to participate in a foster dog program, where they would take dogs (only one a time) for a few weeks. They already have one dog (one that they own) and it's very well trained (I've been over there alone with it when doing repairs and it does not act up). I was thinking of charging an extra pet deposit and allowing this.

Are there any pitfalls in allowing this?