Error handling in webmethod

how can I apply error handling in a webmethod, how can I return ex.Message ?

I have this code for example

<WebMethod()> _
    Public Function SrcTblReg(ByVal SrchTxt As String, ByVal FnameSrctxt As String, _
                                  ByVal SnameSrctxt As String, ByVal TnameSrctxt As String, _
                                  ByVal LnameSrctxt As String, ByVal TelSrcTxt As String, _
                                  ByVal SSNSrcTxt As String, ByVal EmailSrctxt As String, _
                                  ByVal DOBSrcTxt As String)


        Dim constr As String = ConfigurationManager.ConnectionStrings("ARTSQLConStrng").ConnectionString
        Using con As New SqlConnection(constr)
            Using cmd As New SqlCommand("TblRegSearch", con)
                cmd.CommandType = CommandType.StoredProcedure

                If (String.IsNullOrEmpty(SrchTxt)) Then
                    cmd.Parameters.Add("@Searchtxt", SqlDbType.NVarChar).Value = DBNull.Value
                Else
                    cmd.Parameters.Add("@Searchtxt", SqlDbType.NVarChar).Value = SrchTxt
                End If
                If (String.IsNullOrEmpty(FnameSrctxt)) Then
                    cmd.Parameters.Add("@Fname", SqlDbType.Int).Value = DBNull.Value
                Else
                    cmd.Parameters.Add("@Fname", SqlDbType.NVarChar).Value = FnameSrctxt
                End If
                If (String.IsNullOrEmpty(SnameSrctxt)) Then
                    cmd.Parameters.Add("@Sname", SqlDbType.Int).Value = DBNull.Value
                Else
                    cmd.Parameters.Add("@Sname", SqlDbType.NVarChar).Value = SnameSrctxt
                End If
                If (String.IsNullOrEmpty(TnameSrctxt)) Then
                    cmd.Parameters.Add("@Tname", SqlDbType.Int).Value = DBNull.Value
                Else
                    cmd.Parameters.Add("@Tname", SqlDbType.NVarChar).Value = TnameSrctxt
                End If
                If (String.IsNullOrEmpty(LnameSrctxt)) Then
                    cmd.Parameters.Add("@Lname", SqlDbType.Int).Value = DBNull.Value
                Else
                    cmd.Parameters.Add("@Lname", SqlDbType.NVarChar).Value = LnameSrctxt
                End If
                If (String.IsNullOrEmpty(TelSrcTxt)) Then
                    cmd.Parameters.Add("@TelMob", SqlDbType.Int).Value = DBNull.Value
                Else
                    cmd.Parameters.Add("@TelMob", SqlDbType.NVarChar).Value = TelSrcTxt
                End If
                If (String.IsNullOrEmpty(SSNSrcTxt)) Then
                    cmd.Parameters.Add("@SSnum", SqlDbType.Int).Value = DBNull.Value
                Else
                    cmd.Parameters.Add("@SSnum", SqlDbType.NVarChar).Value = SSNSrcTxt
                End If
                If (String.IsNullOrEmpty(EmailSrctxt)) Then
                    cmd.Parameters.Add("@Email", SqlDbType.Int).Value = DBNull.Value
                Else
                    cmd.Parameters.Add("@Email", SqlDbType.NVarChar).Value = EmailSrctxt
                End If
                If (String.IsNullOrEmpty(DOBSrcTxt)) Then
                    cmd.Parameters.Add("@DOB", SqlDbType.Date).Value = DBNull.Value
                Else
                    Dim DOBDte As DateTime = String.Format("{0:dd-MMMM-yyyy}", DOBSrcTxt)
                    cmd.Parameters.Add("@DOB", SqlDbType.Date).Value = DOBDte
                End If
                cmd.Connection = con
                con.Open()
                    Dim ds As New DataSet()
                    Using sda As New SqlDataAdapter(cmd)
                        sda.Fill(ds, "TblRegSrc")
                    End Using
                    con.Close()
                    Return ds.GetXml()
                End Using
        End Using
    End Function