Cloaking Circuits will allow the TARDIS to turn invisible while at the same time using a very low amount of fuel to stay cloaked. The option could be put into the TARDIS monitor as "Toggle Cloak." It could also be accessed in the sonic screwdriver. When the TARDIS is in cloak it shouldn't be able to take-off until it is de-cloaked. Players should also still be able to bump into the TARDIS while it is cloaked.