What platform are you running your application on? According to the documentation, place_tabs_bottom only works on android.
As for how to display or hide the tabbar depending on the model, one way would be to create a module to hold the common tabbar creation code, include it in your controllers and use the before filter to show or hide the tabbar as required. It could look something like this:
module TabbarHelper def show_tabbar ... end def hide_tabbar ... end end
class Model1Controller < Rho::RhoController include TabbarHelper before do |params,request| show_tabbar end end
class Model2Controller < Rho::RhoController include TabbarHelper before do |params,request| hide_tabbar end end