Continuous repel system now in Emerald, for some reason none of Emerald hack really implement this, including decomp hack, they instead give you a box to choose a repel.
It won't work on some emulator, will softlock after use a repel. They are:
Newer VBA-rr
VBA-Next
Older VBA-M less than 2.1.1
(As well as older GBA.emu)
mGBA, MyBoy works fine, other emulator such as Delta (iOS) I don't know.