I would stay away from the Fort Knox. I was looking for the safest possible defense to 1.e4 and became enchanted by the name.
Ohh..."Fort Knox"....now that IS solid. So, I gave it a go for about 10 games.
My growing feeling was that the Fort Knox is just a nice sounding name for meak, passive defense.
Hopefully I can make the difference between "passive" defense and active but "solid" defense clear...
Imagine one boxer hammering away at an opponent who just keeps his gloves over his face, curled up in the corner waiting for the bell to end the round; that's passive defense.
Now imagine the defending boxer is standing up toe-to-toe with his attacker. He blocks the probing jabs and keeps his feet moving...waiting for an opening to appear.
The defender doesn't try to throw any 'knockout' punches but simply stays mobile and looks for the gaps.
When the other guy finally throws that big left hook, he quickly ducks aside and puts a body shot into the guys ribs.
He then backs away (one good body blow is enough for now) and it all starts again.
After about 9 rounds of this, the attacker is worn down and his punches are no longer dangerous.
Now the defender starts to think about a knockout.
Patiently waiting to counterpunch when the other guy commits himself is
solid (since you don't take any big risks)
but still active since keep your feet moving, counterpunch when you can, and don't just stand there.
My experience in the Fort Knox line is that white gets easy play and a very natural initiative that flows right into an inevitable kingside attack. Basically, black doesn't challenge white at all and the defense lacks real counter-punch capability. Black simply curls up in a ball and hopes white cannot use his initiative effectively.
Believe me, white isn't going to just forget you're there and go away.
If anything you just put up a red flag that says "Attack me! I hate to be attacked and I won't try to hurt you!"
For some defenders this is good, provactive chess. The 'rope-a-dope' style of early Korchnoi.
But for most players, its just a bad idea and a miserable way to spend a couple of hours.
"Can he mate me now? .... How about if he goes there?... What happens if he sac that f-pawn? .... Can he mate me now?"
I would therefore recommend a more active defense to 1.e4. A defense that is still
solid in that it that don't involve things like gambiting to steal the initiative (Icelandic Gambit), opposite sides castling (the Dragon) or playing ...f5 and ...g5 opening the position up and turing it into a "who will get there first" contest.
That's easy to say (at least for me) but of course there is no easy solution.
Many, many players have struggled with the 'solid defense to 1.e4 problem (it really is a rather good move to start with) and no one has a clear solution or a "best answer". Some people will assure its the Caro-Kan, others swear by the French, and of course there is the Petroff or the Spanish. All of them are valid tries and all of them deserve respect.
But since I have no idea what types of positions you like to play or what your playing strength is... lets just say that I think you should steer clear of Fort Knox and other "hide under the bed" defenses.
Go for a more active defense which challenges white and doesn't involve waiting for the hammer to fall and hoping it will miss anything important.
Cheers,
Nietzsche