How to validate and prevent Duplicate record insertion in Database using ASP.Net

This Way:

<form id="form1" runat="server">
    <div>
        <asp:TextBox ID="txtName" runat="server" />
        <asp:Label ID="lblMessage" Text="" runat="server" />
        <asp:Button ID="btnSave" runat="server" OnClick="Save" Text="Save" />
    </div>
    </form>

C#:

protected void Save(object sender, EventArgs e)
    {
        string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;

        using (SqlConnection con = new SqlConnection(constr))
        {
            using (SqlCommand cmd = new SqlCommand("SELECT * FROM Person WHERE Name = @Name", con))
            {
                using (SqlDataAdapter da = new SqlDataAdapter(cmd))
                {
                    con.Open();
                    cmd.Parameters.AddWithValue("@Name", this.txtName.Text.Trim());
                    DataSet ds = new DataSet();
                    da.Fill(ds);
                    if (ds.Tables[0].Rows.Count > 0)
                    {
                        this.lblMessage.Text = "Duplicate Entry";
                    }
                    else
                    {
                        using (SqlConnection con2 = new SqlConnection(constr))
                        {
                            using (SqlCommand cmd2 = new SqlCommand("INSERT INTO Person VALUES(@Name)", con2))
                            {
                                con2.Open();
                                cmd2.Parameters.AddWithValue("@Name", this.txtName.Text.Trim());
                                cmd2.ExecuteNonQuery();
                                con2.Close();
                            }
                        }
                        this.lblMessage.Text = "Data Inserted";
                    }

                }
            }
        }

    }

Thank You.