In controller.rb:

def create
  begin
    @client = Client.new(params[:client])
  # Catch the exception from AR::Base
  rescue ActiveRecord::MultiparameterAssignmentErrors => ex
    # Iterarate over the exceptions and remove the invalid field components from the input
    ex.errors.each { |err| params[:client].delete_if { |key, value| key =~ /^#{err.attribute}/ } }
    # Recreate the Model with the bad input fields removed
    @client = Client.new(params[:client])      
  end
    
  if @client.save
    flash[:notice] = 'Client was successfully created.'
    redirect_to :action => 'list'
  else
    init_client_lookup_tables
    render :action => 'new'
  end
end

In model.rb:

validates_presence_of :date_field_name, :message => 'must be a valid date'