<% tracker_ids = @custom_field.tracker_ids %>
<% Tracker.sorted.each do |tracker| %>
<%= check_box_tag "custom_field[tracker_ids][]",
tracker.id,
tracker_ids.include?(tracker.id),
:id => "custom_field_tracker_ids_#{tracker.id}" %>
<% end %>
<%= hidden_field_tag "custom_field[tracker_ids][]", '' %>