It is likely they will still search you (but often this will stop them, because they know the evidence would be worthless).
Maintain that you decline to let them (without threatening). In fact, all you have to do is simply tell the truth: you do not want anyone to search you (for the same reason they probably don't want you to search them!).
The evidence they find will almost certainly never make it to court.
Quoted from some law firms site (advertising primarily to DUI and domestic violence defendants)
10. What if I feel that the police violated my constitutional rights? A criminal defense attorney seeks to exclude evidence obtained as a result of police misconduct. At times, police misconduct occurs in searches that take place during ordinary traffic stops or in a suspect's home. Additionally, if law enforcement is too aggressive in trying to obtain an incriminating statement from a suspect, it may violate the suspect's Miranda rights. Litigation in the criminal court allows a defense lawyer to protect his client's rights by submitting motions to the judge seeking to exclude the recovered evidence or received statements from trial. Often a successful motion to suppress evidence cripples the prosecutor's case, causing the case to either be dismissed or substantially reduced in plea negotiations.
of course, you should throughly study
http://www.flexyourrights.org of course #2: if they do find something, and try to exploit your embarrassment and pounding heart rate, remember to exercise your right to remain silent and demand a lawyer. if you don't the cops will probably trick you into some kind of confession. even if you think you have the perfect lie, just shut the fuck up. you will win zero points for "cooperation." They are trained to lie and question and manipulate in such a way that "anything you say can and will be used against you." Also, they don't need to tell you that stuff anymore. You just have to know it. And know it so hard that, despite your body telling you to submit, use your brain to politely shut the fuck up and they will obviously "understand" why.