Some filter examples for preventing editing of certain users.

gistfile1.php

<?php
/**
 * Prevent Editing of a specified user
 * 
 * This example shows how you can protect the original admin from being edited or deleted by anyone else
 */
add_filter('map_meta_cap', 'prevent_user_edit', 10, 4 );
function prevent_user_edit( $required_caps, $cap, $user_id, $args ){

	$protected_user = 1; // ID of user not editable
	
	if ( $user_id === $protected_user ) // Don't block caps if current user = protected user
		return $required_caps;

	$blocked_caps = array(
		'delete_user',
		'edit_user'
		);
	if ( in_array( $cap, $blocked_caps ) && $args[0] === $protected_user )
		$required_caps[] = 'do_not_allow';

	return $required_caps;
}

gistfile2.php

<?php
/**
 * Prevent Editing of an array of users
 */
add_filter('map_meta_cap', 'prevent_users_edit', 10, 4 );
function prevent_users_edit( $required_caps, $cap, $user_id, $args ){

	$protected_users = array(1,4,19); // IDs of users not editable
	$allowed_editor = 1; // ID of user who can edit
	
	if ( $user_id === $allowed_editor ) // Don't block caps if allowed editor
		return $required_caps;

	$blocked_caps = array(
		'delete_user',
		'edit_user'
		);
	if ( in_array( $cap, $blocked_caps ) && in_array( $args[0], $protected_user ) )
		$required_caps[] = 'do_not_allow';

	return $required_caps;
}