I don't know use Magikarp
Go beat the 6th gym leader ^^, that is in Fortree City.
go to the 5 gym
simply go back to petalburg where your father is gym leader and you must challenge him
first of all its Sapphire after you beat the 5 gym leader go to Wally's house in pettleburg and his dad will give you surf it will work on emerald and ruby no glitch or hack neccicary
in the gym
Go to the right side of the room when you first get in the gym. Then go all the way to the top of the room. Take 5 steps to the left. Go as far south as possible. Go as far left as possible. Take two steps south. Go right until you get to the gym leader.
saffron city (psychic type gym leader)
You answer 5 questions in the radio tower in goldenrod city,she'll talk to you and go back into her gym.
in petalburg city
after you beat 4 to 5 gym leaders you can face him
Gym leader 1. Roark (rock) Gym leader 2. Gardenia (grass) Gym leader 3. Fantina (ghost) Gym leader 4. Maylene (fight) Gym leader 5. (Crasher) Wake (water) Gym leader 6. Byron (steel) Gym leader 7. Candice (ice) Gym leader 8. Volkner (electric) I hope I helped you. =)
The 8th gym can be found in Sootopolis. Who is managed by Juan(uses water type). Hints: Juan has 5 pokemons which is: Luvdisc(be careful by its ATTRACT) Kingdra Sealeo Whiscash crawdaunt