In reality you can’t really refuse the search. Cops have the power, they get to do what they want.
What you do is tell the cop that you do not consent to the search. Do it civillily and respectfully, calmly cite your Constitutional right from unreasonable search and seizure, ask him what his probable cause is, ask him to first get a warrant.
But don’t physically interfere with the search. Just make sure your Ts are dotted and Is crossed for the complaint and lawsuit you’ll file after the search is conducted.
Better call Saul.
Once you refuse a search and a cop still searches a good criminal defense attorney can have any evidence thrown out of court. If there was any.