This is probably the best strategy for catching rayquaza, groudon and kyogre.

Now the TM Skill Swap, I think is terrible.
And if you are having trouble catching the legendries, waste it. For that's what I did.

Now
Step 1:

Catch a Banette in Sky Pillar. I think for Sapphire users you may need to catch its pre-evolution then evolve it

Step 2:

Teach it Skill Swap

Step 3: Engage it in battle and use skill swap!

It's as easy as that!
The reason the pokemon cant use rest is because Bannete's special ability is INSOMINIA (forgive me for spelling errors).
That means the pokemon cannot sleep
SO when you foe uses rest, it's hp wont go up because it cant get to sleep!!!
How's that!

I'm a new member, please could you tell me if this was a good post

And i like it when Rayquaza uses rest, it is a lot easier to catch.

Rayquaza keeps the same skill, i told you!
I did it!