tasks_controller.rb

# Current way of overwriting your create behaviour when the task can't be saved with success:
class TasksController < InheritedResources::Base
  # Project.find_by_title!(params[:project_title]).tasks
  belongs_to :project, :finder => :find_by_title!, :param => :project_title

  def create
    # create! == super
    create! do |format|
      unless @task.errors.empty?
        format.html { redirect_to project_url(@project) }
      end
    end
  end
end

# New way, proposed by grosser!
#
class TasksController < InheritedResources::Base
  # Project.find_by_title!(params[:project_title]).tasks
  belongs_to :project, :finder => :find_by_title!, :param => :project_title

  def create
    # create! == super
    create! do |success, failure|
      failure.html { redirect_to project_url(@project) }
    end
  end
end

# If you want to overwrite both success and failure at once, give me just one block! :)