An easy way of Latias/Latios is by using a Wobbuffet/Wynaut. Their ability is Shadow Tag and it doesnt allow the enemy to escape, it is much better than using mean look.
When you catch Latias/Latios i suggest you go to the move tutor and teach it dragonbreath. they also learn recover at level 45.
We have more cheats and tips for this game here, Pokemon Sapphire cheats
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