You don't need intellectual property protection on the model. You can just contractually require exclusivity.

Insert a clause into the contract with your client that says "you have the right to use this software provided you do not re-use/copy/blah/blah the deep learning model in any way other than as specified in ____. This condition is of the essence, and monetary redress for breaking this term may be insufficient."

If you want to, you can add a watermark to your model for each customer (a special image or something where your classifier gives a totally unique output), then you can tell which customer leaked it, and sue them for contract violation.