Where to put the 'HtmlEncode' on a page?

Where is the best place to htmlEncode a text box on an aspx page? Inside of a Subroutine, between html head tags, between html body tags...?

I want that the content of the text box is HtmlEncode before the data reaches to the server so that no damage is caused. I only knows that it is recommended 'HtmlEncode' all the input strings for security reasons, I understand all the text box fields that in its server validation allows the characters '<' and '>'.

For example: (Where I have to write this?)

Code:

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Dim var1 As String
var1 = mail.Text()
Server.HtmlEncode(var1)

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Thank you,
Cesar

Here is a class with some basic html formatting options I use in all my pages:

Code:

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using System;
using System.Web;
using System.Text.RegularExpressions;

namespace DevTrack.Common.Utils {
        /// <summary>
        /// Helper class for common html functions
        /// </summary>
        public class HtmlHelper {
                /// <summary>
                /// HtmlEncodes the source text
                /// </summary>
                public static string Encode(string value) {
                        return HttpContext.Current != null
                                ? HttpContext.Current.Server.HtmlEncode(value) : value;
                }
                /// <summary>
                /// HtmlDecodes the source text
                /// </summary>
                public static string Decode(string value) {
                        return HttpContext.Current != null
                                ? HttpContext.Current.Server.HtmlDecode(value) : value;
                }
                /// <summary>
                /// Removes Html & Xml tags from the source text
                /// </summary>
                public static string StripHtmlXmlTags (string content) {
                        return Regex.Replace(content, "<[^>]+>",
                                String.Empty, RegexOptions.IgnoreCase | RegexOptions.Compiled);
                }
                /// <summary>
                /// Removes script tags from the source text
                /// </summary>
                public static string StripScriptTags(string content) {
                        return  Regex.Replace(content, "<script((.|\n)*?)</script>",
                                String.Empty, RegexOptions.IgnoreCase | RegexOptions.Multiline);
                }
        }
}

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