enforcing no pet clause in Santa Monica

[Scott Malkin]

We have a tenant who has lived in his apt for ~ 2yrs, lease has a 'no pet clause', tenant has had a dog for nearly their entire tenancy. We would like to now enforce the no pet clause. I understand that one could argue we waived our right to enforce the clause as a long period has passed. The previous owner (family member who  passed away ~ 6 months ago) did not enforce clause. We, the new owners,  have  just recently become aware of the dog (2 months ago) and just recently (one week ago) found the old lease with the pet clause we would now like to enforce it. Do you think we would prevail if tenant challenges this in court? This is a rent-controlled apartment in Santa Monica....