I don't know of a router feature that would prevent searches for key words.
However you can build a policy map that evaluates a class map that in turn looks for regular expressions in the http URL and headers. This is highly dependant on the hardware, feature set and IOS version. Use the Cisco feature navigator or contact a sales engineer to see if this would be available for you.
The 'match protocol http' command reference follows:
#########
match protocol http
To configure Network-Based Application Recognition (NBAR) to match HTTP traffic by URL, host, Multipurpose Internet Mail Extension (MIME) type, or fields in HTTP packet headers, use the match protocol http command in class-map configuration mode. To disable NBAR from matching HTTP traffic by URL, host, or MIME type, or fields in HTTP packet headers, use the no form of this command.
Cisco IOS Release 12.4(24)T and Earlier Releases, Cisco IOS Release 12.2(33)SRA, Cisco IOS Release 12.2(14)S and Later Releases
match protocol http [url url-string | host hostname-string | mime MIME-type | c-header-field c-header-field-string | s-header-field s-header-field-string]
no match protocol http [url url-string | host hostname-string | mime MIME-type | c-header-field c-header-field-string | s-header-field s-header-field-string]
Cisco IOS Release 15.1(2)T, Cisco IOS XE Release 3.1S and Later Releases and Catalyst 6500 Series Switch Equipped with the Supervisor 32/PISA Engine
match protocol http [content-encoding content-encoding-name-string | from from-address-string | host hostname-string | location location-name-string | mime MIME-type | referer referer-address-string | server server-software-name-string | url url-string | user-agent user-agent-software-name-string]
no match protocol http [content-encoding content-encoding-name-string | from from-address-string | host hostname-string | location location-name-string | mime
MIME-type | referer referer-address-string | server server-software-name-string | url url-string | user-agent user-agent-software-name-string]
Syntax Description
Command Default
NBAR does not match HTTP traffic by URL, host, MIME type, or fields in HTTP packet headers.
Command Modes
Class-map configuration (config-cmap)
Command History
Usage Guidelines
Classification of HTTP Traffic by Host, URL, or MIME
In Cisco IOS Release 12.3(4)T, the NBAR Extended Inspection for HTTP Traffic feature was introduced. This feature allows NBAR to scan TCP ports that are not well-known and that identify HTTP traffic traversing these ports. This feature is enabled automatically when a service policy containing the match protocol http command is attached to an interface.
When matching by MIME type, the MIME type can contain any user-specified text string. See the following web page for the IANA-registered MIME types:
http://www.iana.org/assignments/media-types/
When matching by MIME type, NBAR matches a packet containing the MIME type and all subsequent packets until the next HTTP transaction.
When matching by host, NBAR performs a regular expression match on the host field contents inside the HTTP packet and classifies all packets from that host.
HTTP client request matching supports GET, PUT, HEAD, POST, DELETE, OPTIONS, CONNECT, and TRACE. When matching by URL, NBAR recognizes the HTTP packets containing the URL and then matches all packets that are part of the HTTP request. When specifying a URL for classification, include only the portion of the URL that follows the www.hostname.domain in the match statement. For example, for the URL www.cisco.com/latest/whatsnew.html, include only /latest/whatsnew.html with the match statement (for instance, match protocol http url /latest/whatsnew.html).
Note 
For Cisco IOS Release 12.2(18)ZY2 (and later releases) on the Cisco Catalyst 6500 series switch that is equipped with a Supervisor 32/PISA, up to 56 parameters or subclassifications per protocol per router can be specified with the match protocol http command. These parameters or subclassifications can be a combination of any of the available match choices, such as host matches, MIME matches, server matches, and URL matches. For other Cisco IOS releases and platforms, the maximum is 24 parameters or subclassifications per protocol per router.
To match the www.anydomain.com portion, use the hostname matching feature. The parameter specification strings can take the form of a regular expression with the following options.
Classification of HTTP Header Fields
In Cisco IOS Release 12.3(11)T, NBAR introduced expanded ability for users to classify HTTP traffic using information in the HTTP Header Fields.
HTTP works using a client/server model: HTTP clients open connections by sending a request message to an HTTP server. The HTTP server then returns a response message to the HTTP client (this response message is typically the resource requested in the request message from the HTTP client). After delivering the response, the HTTP server closes the connection and the transaction is complete.
HTTP header fields are used to provide information about HTTP request and response messages. HTTP has numerous header fields. For additional information on HTTP headers, see section 14 of RFC 2616: Hypertext Transfer Protocol—HTTP/1.1. This document can be read at the following URL:
