SQL Null Values In VB

I have tried doing a search, as I figured this would be a common problem, but I wasn't able to find anything.  I know that my SP is functional because when I use VWD execute the query outside of the webpage, I get the correct results -however I have to ensure that a field is either entered, or set to <NULL>.  In my SET's I want it to use the wildcards.

What I want is to do a search (plenty of existing topics on that, however none were of help to me).  If a field is entered, then it is included in the search.  Otherwise it should be ignored.  In my VB I have the standard stored procedure call, passing in values to all of the parameters in the stored proc below:

CREATE PROCEDURE dbo.SearchDog
@tagnum int,
@ownername varchar(50),
@mailaddress varchar(50),
@address2 varchar(50),
@city varchar(50),
@telephone varchar(50),
@doggender varchar(50),
@dogbreed varchar(50),
@dogage varchar(50),
@dogcolour varchar(50),
@dogname varchar(50),
@applicationdate varchar(50)
AS
 IF @tagnum=-1
  SET @tagnum=NULL
  SET @ownername = '%'+@ownername+'%'
  SET @mailaddress = '%'+@mailaddress+'%'
  SET @address2='%'+@address2+'%'
  SET @city = '%'+@city+'%'
  SET @telephone='%'+@telephone+'%'
  SET @dogcolour='%'+@dogcolour+'%'
  SET @dogbreed='%'+@dogbreed+'%'
  SET @dogage='%'+@dogage+'%'
  SET @doggender='%'+@doggender+'%'
  SET @dogname='%'+@dogname+'%'
  SET @applicationdate='%'+@applicationdate+'%'

 SELECT DISTINCT  *
 FROM DogRegistry
 WHERE (
  TagNum = @tagnum OR
  OwnerName LIKE @ownername OR
  MailAddress LIKE @mailaddress OR
  Address2 LIKE @address2 OR
  City LIKE @city OR
  Telephone LIKE @telephone OR
  DogGender LIKE @doggender OR
  DogBreed LIKE @dogbreed OR
  DogAge LIKE @dogage OR
  DogColour LIKE @dogcolour OR
  DogName LIKE @dogname OR
  ApplicationDate LIKE @applicationdate
  ) AND TagNum > 0
GO


I don't know why it is creating links inside my SP -ignore them.  TagNum is the primary key, if that makes a difference.

On the webpage, it ONLY works when every field has been filled (and then it will only return 1 row, as it should, given the data entered).  Debugging has shown that when nothing is entered it passes "".

Any ideas?