client.rb

class Client < ActiveRecord::Base

  acts_as_paranoid

  has_many :client_users, :dependent => :destroy
  has_many :users, :through => :client_users

client_user.rb

class ClientUser < ActiveRecord::Base

  acts_as_paranoid

  belongs_to :client
  belongs_to :user

user.rb

class User < ActiveRecord::Base

  acts_as_paranoid

  has_many :client_users, :dependent => :destroy
  has_many :clients, :through => :client_users