They already explained it.

[Marysara1]

https://www.msn.com/en-us/entertainment ... a9a2&ei=15 His first wife Shannon had the rules.The team asked his father about the rules and he didn't know what they were talking about. There was a flashback of Gibbs meeting Shannon. She was the one that had all the rules.

[Masha]

I believed that his greatest secret is how he got the boats out of his basement.

[Marysara1]

I believed that his greatest secret is how he got the boats out of his basement.

Before he left ,he told Torres how he got the boat out.