This country urgently needs a policy regarding captive exchanges. Once, we had one: It was no negotiations with terrorists. Period. That has morphed today into absurd horse-trading of the "any price" variety, including 20 female terrorists for a videocassette. Hopefully one day very soon Gilad Schalit will be released. That will be a wonderful occasion, and it's too late to reformulate our policy this time around. Because freeing hundreds of criminals encourages future kidnappings, however, the policy must indeed be changed immediately following Schalit's return. Israel must give its answer - unequivocally and in advance - to Hamas leader Khaled Mashaal, who tellingly observed recently in Damascus: "We are capable of capturing Schalit and Schalit and Schalit until there is not even one prisoner in the enemy's jails." This challenge is daunting precisely because it sets Israelis not against Hamas but rather each person against himself. We are profoundly torn. Each of us is a parent or grandparent who would pay any price to gain the release of a child. Thankfully, our society views Gilad Schalit not as expendable cannon fodder but precisely as our own flesh and blood. But each of us is also a potential victim of terror, a potential kidnappee. As such, we realize fully that surrendering to extortionists' wild demands may secure a videotape or the remains of long-deceased MIAs or even a live soldier - but at the crystal-clear cost of encouraging many more attempts by Hamas to kidnap other Jews. This is an untenable position in which we dare not wallow passively. REFLECTING THIS latter perspective, I recently had a very difficult conversation with two fathers in Tel Aviv, each of whom had lost a child to terrorists. They oppose the release of any Palestinian prisoners for any Israeli. They know their position is an unpopular albeit principled one, and they asked my advice on how to communicate it persuasively to the public. It was my unenviable task to tell them it just wouldn't fly. Emotionally, pitted against the release of a real, live young Israeli, rejection of negotiations just cannot capture public support. Yet neither is the public in love with the idea of releasing up to 1,000 hardened criminals, many with blood on their hands. One for one. The thought came to me in a flash. Somewhere between zero and 1,000 lies this wholly sane, compelling formula. Think about it: We do in fact oppose negotiating with terrorists. Trading any terrorist for any Israeli is a disgusting thought. Yet there is a compelling logic to the principle of "one for one," which is intellectually intuitive and could not be morally clearer. On the same day Schalit comes home, Israel should announce its new unyielding and ironclad policy: We will do everything possible to prevent future kidnappings, and our policy remains not to reward terrorists for their crimes. However, the most we will ever agree to under any circumstances in any future exchange will be one. We can negotiate over the who in such a case, but never on the how many. This should be codified by legislation. I know this, too, will raise questions. Some will argue, with justification, that releasing even one evil person to win the release of an innocent is one too many. There can be no moral equivalency between the terrorist and the one defending against the terrorist. Others will say we dare not tie the government's hands, so no stratagem should be written in stone. If we need to free five bad guys at some point, or 50 or 500, then let the leaders make that determination as the situation warrants. That is precisely my point: It is the situation that is not written in stone, while the principles must be. Not very long ago, civilians in Jerusalem's Gilo neighborhood were being constantly shot at. Buses were being blown up in the streets of Tel Aviv and Haifa. Rockets were pouring onto the homes in Sderot. Suicide bombers seeped into our cities, seemingly unchecked. These bloody attacks have largely ceased. Effective intelligence contributed mightily, but so did changes in public policy. Many fires were quashed as a result of wise, effective counter-measures. Changes were implemented, and they worked. Hamas has managed to kidnap one solitary soldier and hold him. It's not an easy thing to do. Further attempts will follow, but a new policy of "one for one" will dampen the Palestinians' penchant for even trying. If they know that even a successful kidnapping will result at very most in only one, not 1,000 released prisoners, they will abandon the tactic. What the security wall has become to untold dozens of would-be mass murderers, "one for one" can be to those who plot future kidnappings. We absolutely must stand firm. The writer is a media and public affairs consultant based in Jerusalem.