If Donphan is your lead, I would concider Stealth Rock, and if I know you, you will use him as your lead
Ice Fang, and Fire Fang are a good choce, Earthquake aswell, though Stone Edge can be used, other than that, a good setup.
Steelix, suprisingly can learn Rest, a chesto Rest Steelix could prove well as a wall, Earthquake, Iron Tail and Aqua Tail are all good moves, not sure about Thunder Fang maybe Gyro Ball...I find it hard to find good setups for Steel pokemon.
Rhyperior has fairly high HP so a Sword Damce or two wouldn't be a problem getting in battle, Stone Edge would be a good choice thanks to it's massive Attack stat, Thunder Punch would do nothing unless you EV'd it's SP Attacl stat also Rest and Sleep Talk would be a good support poke. Roar actualy has a purpose in competative battling so it might be a nice move to keep in mind.
Flygon is a very balanced pokemon, lots of ways to use him, U-Turn is an over used move for him as it is very effective, also Roost as it helps in alot of cases. Fire Blast gets used alot over Heat Wave due to damage, only a 5% less chance to hit but with the extra power who's complaining. Toxic might be an idea just to pick at your enemys and Draco Meteor as you said, very nice choice.
As metagross is pretty slow, Agility could be the way to go, there is something people call the ' Agiligross ' the movepool cosists of Agility, Meteor Mash, Earthquake and Tunder Punch/Ice Punch. Or Explosion.
He has alot of power behind him, and type is your advantage with him so use him wisely Try and give him the HP EV's he needs though, for longer lasting results.
And finaly Garchomp Outrage or Dragon Claw are a must for him as they are one of his most powerful moves. Stone Edge could help alot, and as he is pretty quick, Sword Dance may be a good idea for even higher attack.
I would go with Earthquake, Dragon Claw, Stone Edge and Sword Dance.
Now I noticed that every move you have are attack moves, it might be a ground team, therefore alot of power and defence behind the team but a good Starmie or Empoleon would really take out alot of your best pokes there.
My suggestion is finding a team that has support moves aswell as power, Instead of your beloved Donphan, may I suggest Hippowdon, and a couple of good idea's for ground types would be Torterra and Swampert, maybe ditch your Garchomp/Flygon over one of them. Also Gliscor is a very anoyying pokemon to take down due to it's high speed and defence.
Another pokemon you could take in to concideration would be Claydol, he can be used in so many ways for support, for example, Reflect and Light Screen are very nice for a ground team, He can learn Stealth Rock, Toxic, Explosion, and even Rest and Sleep Talk, so he can be used to your advantage if you find yourself stuck somehow.
That is my advice for you team, I hope I helped.