AccountsController

  before_filter :correct_user, only: :show

  def correct_user
    @account = Account.find_by_id(params[:id])
    redirect_to root_url unless correct_user?(@account.user_id)
  end

routes.rb

LifeUlator::Application.routes.draw do

  root :to => "users#new"
  resources :sessions, only: [:new, :create, :destroy]
  
  resources :users
  resources :accounts
  
  
  match '/signin', to: "sessions#new"
  match '/signout', to: "sessions#destroy"
end

SessionsHelper

module SessionsHelper
  
  def current_user
    @current_user ||= User.find(session[:user_id]) if session[:user_id]
  end
  
  def registered_user
    unless current_user
      redirect_to root_url
    end
  end
  
  def correct_user?(user)
    user == current_user
  end
  
end