Captcha Code in order to return entries in SLP?

We are very cautious about giving away our list, and were looking for a way to make sure that someone wasn’t able to get our complete list. I’ve already restricted the radius of a user’s search, and set it so that only 4 search results are returned at a time. Is there any way to make it even more secure by adding a captcha code to the page? Thanks so much!

https://www.ads-software.com/extend/plugins/store-locator-le/