get some heat shtink @ radio shack that will fit over the connectors, cut about 1&1/2" & slip it over one side of the connector, pulg your extension to the servo, slide the heat shrink over the connection & center it so it will fully cover the entire connection & shrink it. I have done this on several planes & have never had one come apart. In fact I was recently stripping a crashed plane & had to cut the heat shrink with a hobby knife & it was not an easy task as it gets pretty hard after it is shrunk.

Gil