Hi.  Your best bet is to use the "sp_helpprotect" system stored procedure.  Here is the syntax (from Books Online):

sp_helprotect [ [ @name = ] 'object_statement' ]

    [ , [ @username = ] 'security_account' ]

    [ , [ @grantorname = ] 'grantor' ]

    [ , [ @permissionarea = ] 'type' ]

In your case, you would use:

"sp_protect 'stored_procedure_name'"

For these types of questions, books online is by far the best resource there is.  In fact, if you click the index tab and type in sp_helpprotect, it will go into a lot more detail about its use and what not.  I hope this helps.

Thanks,

Eric