XXXManager

Nope. It will not be efficient and will not work really..
See what I suggested above and what greedinc wrote. He has hundrads of attacking domains (which sounds strange to me but anyway).. therefore what you wrote wont help him.

greedinc: I don't know why I am helping you with this since you are "saying" you are attacked by bad guys BUT you are not willing to say which URLs the attackers use and which URLs of yours they attack. I don't understand what you have to hide it you claim to be a legit player. Can you explain? Are you doing CP or other illegal stuff??
Well, I guess I am helping you because you MIGHT be telling the truth in a way and for the chance that this is the case - I am willing to help.

If you have 100s of domains attacking do this...
Create a map file with pairs of the attacking domains and the word NWJ (acronyms of "No Way Jose") ;)
like that...
http://www.attacker1.com NWJ
http://www.attacker2.com NWJ
etc..

Enable mod_rewrite it its not yet enabled on your webserver.
Set a "RewriteMap NWJMap txt:/path/to/NWJ.dat"

break down the %{HTTP_REFERER} with a REGEXP rewrite condition and get the first part up to the THIRD backslash (Not including) leaving you with the http://......com in $1

Do a "RewriteCond ${NWJMap:$1} ^NWJ$"

Do a rewrite rule to http:// so that the client will show 404 for the onject.

- Paypal donations will not be met with resistance LOL

I redraw from my prior suggestion. do NOT, I repeat - NOT, send the hit back to the attacker.
For 3 reasons:
1. The attacker/s can redirect the rediretion BACK to you and so you will be damaged once again
2. It is illegal - even when he attacks you
3. The attacker/s might be using a third party system or a free host - in that case you will be attacking that system and you will damage innocent people.
Do NOT redirect traffic back to the attackers!!

Hope it helps