I have a 6 string explorer bass.
To stop the neck dive you can do 3 things:
1. Decrease the weight of the neck-headstock (with e.g. lighter tuning pegs)
2. Increase the weight of the body (this is what Ned Steinberger did for the prototypes of Spector bass) or like the strap with weight that link was given (but why on earth would somebody 1. want to add weight to the bass, I don't buy that " 3" wide strap does not let you feel it" thing because I feel every gram on my shoulder no matter how wide is the strap, and 2. why pay that much money where you can easily attach some weight to the body side of a normal strap)
3. Change the witness point of strap (I mean where it is held on neck side). This is what I do, I have a small metal bar leaning towards the neck (and copying the shape of headstock), so the strap is attached almost on the 12th fret. The other pictures shown by other TB'ers have the same idea, and I'd go with that idea. The same idea is used on NS/Bolin basses.
Wearing a wide strap may help to keep it in position to some extent (because the wider the contact area of strap on the shoulder, the bigger friction force, keeping the bass in position) but it is not a pure remedy, of course IMHO
