I assume you want an offensive arcanine moveset:
Flare Blitz
Close Combat
Extreme Speed
Will-o-wisp/Morning Sun/Crunch
The last slot is ur choice, W-o-w cripple Arcanine counters upon switch-in and may let opponents mistake it as defensive set. Morning Sun provide longevity for arcanine during the game, especially good if u're running a Sun team, since the move recover 2/3 max hp under sunlight. Crunch, Thunder Fang or even Outrage provide another coverage move, but personally I think it's not needed. If Wild Charge is available (it's not right now), it maybe a good option for the 4th slot too.
i am with bong you need just to add thunder fang in last slot to counter gyarados