How do I prove marijuana smell left by tenant?

[Amanda Homan]

We had our tenant move out early this month from our rental home in Texas.  The woman who lived there (and/or her guests) were clearly smoking marijuana a lot in the house. We are having the carpets and the house cleaned later this week. However, if we can’t get the smell out, we might have to re-paint and/or replace the carpets. That could run thousands of dollars. We are holding $6k in deposits from her, so we have about $4.5k after we deduct for the ½ month she was there this month. I believe that if we have to replace the carpets and paint she will be very unhappy when we deduct the funds from her deposit. She has maintained all along that no smoking has taken place. We notified her in a letter several months ago that we could smell the marijuana, and it is very clearly stated in the lease that smoking of any kind is not permitted in the home. Here is my question: if we end up in a legal dispute and have to defend/justify our cleaning actions/costs, what proof would you need to show that we were justified in our actions? Meaning, how do we prove there was an overwhelming odor that we had to address in order to re-rent the house? I am trying to avoid a potential he said/she said scenario.