Anyone know how I can enforce a field to be required when overriding the getCMSFields method?

Have a look at this thread:
http://silverstripe.org/data-model-questions/show/257241

Fantastic! Thanks Mad_Clog - that's it...you rock!

...well, you still rock but...unfortunately it does not appear to be working in my situation.

When I added the getCMSValidator, and then attempt to post the new page without the required fields, it just goes ahead and posts without complaint. I am using SS 2.3.7.

Here is the code I am using...

class GatedContent extends Page 
{
	static $db = array(
		'Date' => 'Date',
		'FormID' => 'Varchar(4)',
		'DeployNum' => 'Varchar(10)'
	);

	function getCMSFields() 
	{
		$fields = parent::getCMSFields();
		$fields->addFieldToTab('Root.Content.Main', new DatePickerField('Date'), 'Content');
		$fields->addFieldToTab('Root.Content.Main', new TextField('FormID','Form ID (Required)'), 'Content');
		$fields->addFieldToTab('Root.Content.Main', new TextField('DeployNum', 'Deployment Number (Required)'), 'Content');

		// Remove the widget holders for this content type
		$fields->removeFieldFromTab('Root.Content', 'RelatedMenu');

		return $fields;
	}

	// Enforce FormID and DeployNum as being required
	function getCMSValidator()
	{
		return new RequiredFields('FormID','DeployNum');
	}

	...
	...
}

I just tried it out on the default Page class and everything works as expected

<?php
class Page extends SiteTree {

	public static $db = array(
	);

	public static $has_one = array(
	);

	/**
	 * Add a custom validator
	 * 
	 * @access public
	 * @return RequiredFields
	 */
	public function getCMSValidator() {
		return new RequiredFields('Title', 'MenuTitle');
	}
}
class Page_Controller extends ContentController {

	/**
	 * An array of actions that can be accessed via a request. Each array element should be an action name, and the
	 * permissions or conditions required to allow the user to access it.
	 *
	 * <code>
	 * array (
	 *     'action', // anyone can access this action
	 *     'action' => true, // same as above
	 *     'action' => 'ADMIN', // you must have ADMIN permissions to access this action
	 *     'action' => '->checkAction' // you can only access this action if $this->checkAction() returns true
	 * );
	 * </code>
	 *
	 * @var array
	 */
	public static $allowed_actions = array (
	);

	public function init() {
		parent::init();

		// Note: you should use SS template require tags inside your templates
		// instead of putting Requirements calls here.  However these are
		// included so that our older themes still work
		Requirements::themedCSS('layout');
		Requirements::themedCSS('typography');
		Requirements::themedCSS('form');
	}
}

I think Mad_Clog is using 2.4 above version. ImacSS is using 2.3.7, so give this a try.

in the /cms/code/CMSMain.php line 416 add in following code

//$form = new Form($this, "EditForm", $fields, $actions);
$validator = ($record->hasMethod('getCMSValidator')) ? $record->getCMSValidator() : null;
$form = new Form($this, "EditForm", $fields, $actions, $validator);