Sand Rush should be banned, not Excadrill... ;_; Blaziken agrees with me. =/
So then, let me formally welcome you to the competitive side of Wiichat's 'mon forum, MR.
I loves me some sandstorm team, been usin' said weather teams since the beginning of Gen 4. Their most notable benefit is the raw power they have; powerful pokes and that damn annoying Sandstorm. Their most notable weakness, can be huge collective weaknesses. Your team definitely embodies both.
Four Water weaknesses is just bad, particularly since your Ferro isn't the specially defensive variant. And once it dies, you WILL get swept, whether their team relies on Rain or not. You absolutely need moar Water resistance, and to take that 4x weakness down a notch. Three weakness and two resist is only bareable at best; four simply shouldn't be tolerated. This is a huge problem that needs fixing, otherwise random Starmies will have some lulz, and rain teams will have a walk in the park.
Your Fighting weakness is at 3x weak and 2x resist; pretty much every team throws around nasty STAB fighting attacks, and considering your main physical wall is WEAK to Fighting, this is a problem. Fighting is the most dominant type alongside Dragon in OU I'd say, so you'll need to be more prepared for it. Particularly since TTar is so important to your team. What happens when a rain team's Toxicroak ends your TTar, and permarain rains on your parade, eh?
Your Ground weakness is at three with one resist. That's relatively bad. Ground isn't the omnipotently common attack type it's almost always been since Fighting is almost the same and has replaced it in many ways, but being weak to both is just asking to get sweeped. It's not entirely necessary to patch this up, but if you swap out a poke to remedy your Water and Fighting problem, fixing your Ground problem at the same time would be smart (if possible...).
Aside from that though, you've got a great stock of resistances and some good immunities (your entire team resists or is immune to poison looool). Your team is made of some great pokes with some great moveset synergy, there's no doubt. But your weaknesses stack way too high. Because of this, I believe this team will end up as a "you win some, you lose some". If the opponent doesn't run Pokes that dominate your team (fat chance...), you're definitely giving 'em a run for their money. If they do, you'll probably get shut out right from the get-go, and your chances of winning take a nasty hit.
In other words, you need to patch up those weaknesses to make this team as viable as it can be. To be great, rather than just good. A word of advice in order to pursue this; the most successful Sandstorm teams don't limit themselves to Rock, Steel, and Ground pokes. Dual typing all of your Pokes to these types won't solve your problems. Sandstorm hurting one, two, or even three of your Pokes won't be the end of you, since it's guaranteed your opponent will be taking more damage from the said sandstorm than you will. Let the Sandstorm limit your choices, and your team is therefore limited.
If I had to list a Pokemon to replace, I'd go for Nidoking; but since he's there since you like 'em, I'd imagine that's out of the question, yeah? 'Least it's a lot better than that damn Sharpedo.
Though, really, this is a pretty good team for one hour's thought. Pretty good for your first post too. It's got some holes to patch up, but once they're fixed, I'll certainly approve of it. Damn straight.