Is he talking about transmagnetic stimulation? It isn't all that experimental anymore, but the efficacy is still only about 50% at best. Some insurances cover it; some do not. Your therapist wouldn't be the person doing the treatment; it is done by psychiatrists, so I'm guessing he would be referring you to a psychiatrist who does that treatment. I would simply reiterate to him again that it is not covered by your insurance is is therefore not an option and that the subject needs to be dropped. Many times families will help patients pay for treatments that aren't covered by insurance, but in your case that simply isn't an option; just ask him not to bring it up again.