if you are trying to use it as a physical wall, then you could go with:
Relicanth @ Leftovers
Impish/Relaxed Nature
252 HP/164 DEF/92 ATK
Ability: Rock Head
-Head Smash
-Waterfall/Surf
-Stealth Rock/Calm Mind/Amnesia/Protect
-Yawn/Protect
resttalk is not good on relicanth because of its X4 grass weakness, as well as its common weakness of electric, ground, and fighting. with this set, you can either use it for basic physical set with waterfal + stealth rock + yawn/protect. you can also use calm mind to boost its special stats as well for surf so that it has a chance against other physical walls like hippowdown/skarmory/donphan and for becoming a good offensive wall even against special sweepers. amnesia is an option if you're worried about special sweepers.
if you want to go for a physical sweeper, you can give it Choice Band:
Relicanth @ Choice Band
Adamant Nature
252 ATK/252 HP/4 SPD
Ability: Rock Head
-Head Smash
-Waterfall
-Earthquake
-Stealth Rock/Yawn/Rain Dance
stealth rock/yawn/rain daince are options for using the move and switchout. all strategic. rain dance is an especially nice one since you can switch relicanth out, bring something else in, and then bring relicanth out for the boost of Waterfall.
if you want to have a physical sweeping relicanth but do not want to have to bother with choice band, you can try the following set:
Relicanth @ Liechi Berry/Life Orb
Adamant Nature
252 ATK/32 HP/224 SPD
Ability: Rock Head/Swift Swim
-Head Smash/Stone Edge
-Waterfall
-Earthquake
-Rock Polish/Rain Dance
the combos are rock head + head smash + waterfall + eq + rock polish and the other is swift swim + stone edge + waterfall + eq + rain dance. i know everyone prefers rock head, but swift swim does have an advantage. not only does it double relicanth's speed, but it also boosts Waterfall's power by an additional 50%. while Head Smash has a 225 BP with STAB but 80 accuracy, Waterfall has 100% acc, 20% flinch and 160 BP. also, Waterfall being a water type move is more threatening to a lot of pokes. with Rain Dance up, Waterfall would 2HKO blissey.