From http://www.developingandstuff.com/2014/06/disable-dangerous-rake-tasks-in.html?utm_source=rubyweekly&utm_medium=email

disable_db_tasks_on_production.rake

DISABLED_TASKS = [
  'db:drop',
  'db:migrate:reset',
  'db:schema:load',
  'db:seed',
  # ...
]

namespace :db do
  desc "Disable a task in production environment"
  task :guard_for_production do
    if Rails.env.production?
      if ENV['I_KNOW_THIS_MAY_SCREW_THE_DB'] != "1"
        puts 'This task is disabled in production.'
        puts 'If you really want to run it, call it again with `I_KNOW_THIS_MAY_SCREW_THE_DB=1`'
        exit
      else
        require 'heroku'
        puts 'Making a backup of the database, just in case...'
        puts `heroku pgbackups:capture`
      end
    end
  end
end

DISABLED_TASKS.each do |task|
  Rake::Task[task].enhance ['db:guard_for_production']
end