use a grass Pokemon at about level 42 (u could use electric but then u'd need a different approach against wishcash which is water/ground, his Pokemon are as follows:
Luvdisc (Level 40), Whiscash (Level 42), Sealeo (Level 40), Seaking (Level 42), Milotic (Level 43)
Defeat the eighth gym leader.
In Mossdeep city I think.....
go back to your fathers gym and defeat him
Defeat the 3rd Gym Leader, Wattson, in Mauville City.
To defeat or "beat" the 7th gym leader in Pokemon sapphire there twins and they have a solrock and a lunatone to beat them I suggest about level 40-50 water types.
Go on to defeat the seventh gym in Mossdeep City, if you did not already catch Kyogre.
go to the desert get the fossil and then go to petalburg city and defeat the gym there
The third gym leader in Pokemon Sapphire is Wattson and he is located in Mauville City.
If you mean Pokemon Sapphire, then it is in the house on the west part of the city with the fifth gym. You have to have defeated the gym leader first.
It depends on the version. In Pokemon Ruby, Sapphire, and Emerald, the fifth gym leader is Norman. He specializes in using normal type Pokemon and he is your father. His Pokemon are 2 Vigoroth and 1 Slacking.
defeat the fourth gym leader and when u come out of the gym, may will give u the go-goggles.
Try to use a flying Pokemon or psychic Pokemon, I used Ralts and Taillow to beat him. Yeah so try using flying or psychic.