Why can't I catch the legendary dogs in HeartGold?

I have the legendary dogs at one health and I keep trying to catch them by using Ultra Balls. What am I doing wrong?

Pleaselog inorregisterto add a comment.

You’re not doing anything wrong. But to improve your chances could you use a Pokemon with the moves ingrain and block or mean look. Start by using Mean Look/Block, now they’ll not be able to run from you. Next use ingrain, this block the effect of roar. I used a Smeargle. But you could use other Pokes as well.

This is because the roaming dogs have areallylow catch rate of 3, or 0.4%, with a Pokeball at full health, as seen with Suicunehere. Since you are playing heartgold and not the original, I would suggest using a Dusk Ball (Which has a catch rate of 3.5x if used in a cave on at night), or, better yet, a Quick Ball (Which has a catch rate of 4x if used on the first turn of battle), rather than an Ultra Ball (Which has a catch rate of 2x). Other than that there, there’s nothing more you can but keep trying to catch until it works. Good luck :).

Bulbapedia’s page on Pokeballs, including catch rates

Quick balls are a great option, as they work best when the battle first begins, COMBINED with the fact that they are down to 1 hp, they should be the best option. However, keep in mind that these are legendary Pokémon, so even the best chances are not a guaranteed catch. (I have been using this method for about a month now, to try and catch entei and raikou, with still no success)