E-collars can be great tools, but they are only as good as the user.  Get one that has stimulate, vibrate, and tone modes. Before you zap the dog, review his recall skills on a long line and in a fenced area first.  Does he really understand the command?  Has the command been 'poisoned'?  I think this is a great video about the steps preceding the addition of pressure (eg. e-collar) for recalls. Of particular note are the concepts of superstitious associations and competing motivators.
http://leerburg.com/flix/player.php/819/Can_you_help_me_with_my_recall