I would advise against an assassin as per the class, since they make poor arena fighters.
Are there any restrictions on the type of arena fighter? (magic/ no magic, restriction on weapon/armor)
(i search new spell in complete divine)Righteous Might
Divine Power
Greater Magic Weapon
Magic Vestments
Air Walk
Freedom of Movement
Protection From Energy
Wind Wall
Spell Resistence
1) You're playing a Cleric as a Fighter with buffs, not as a Cleric, when you're doing this build. You're not using any spells with saves, so the Wisdom score of 20 isn't needed. You could get away with a Wisdom of 16 without compromising anything at all (except later advancement - you'll want Wis-17 at 11th, Wis-18 at 13th, Wis-19 at 15th and above). Saved points go into Charisma, Strength, or Con.
2) The build changes based on the rules of the arena. If you've got "safe" rounds you can spend on buffing, you are (for the most part) better off trading Extend Spell, Persistent Spell, and Divine Metamagic(Persistent Spell) for Extra Turning, Quicken Spell, and Divine Metamagic(Quicken Spell), as you basically just need two or three buffs up, and with two rounds to prepare, Quicken spell lets you do that for less cost than Persistent Spell.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.