IIS Rewrite not working while blocking Special characters

I have the following url's using which my site is accessed:

http://www.itsmysitesitesite.com/showproduct.aspx?id=230
http://www.itsmysitesitesite.com/browseproduct.aspx?catid=100

I want to write a IIS Rewrite Rule that blocks a url if the ID= or catid= portion starts with minus (-)

Eg: block these urls

http://www.itsmysitesitesite.com/showproduct.aspx?id=-230
http://www.itsmysitesitesite.com/showproduct.aspx?id=-2%27
http://www.itsmysitesitesite.com/browseproduct.aspx?catid=-1

In my IIS 8.0 I wrote a Rewrite Rule as following:

<system.webServer><security><requestFiltering><denyUrlSequences><add sequence="id=-" /> <add sequence="catid=-" /></denyUrlSequences></requestFiltering></security>

However when I test it using a url say 

http://www.itsmysitesitesite.com/showproduct.aspx?id=-230

a errror gets thrown and the exception is handled. The IIS Rewrite is not working, i.e. it is not blocking the url at the first place.

Can anyone throw some pointers