You put enough of anything between the tx and rx antennae and you will lose your signal.
The satellites put out pretty low power (50 watts according to online source)
From an online GPS info blurb..
Due to their high frequency, GPS signals cannot permeate stone or water. Even a thick foliation in forests may attenuate the signal to an extent that some (mainly older) GPS receivers have difficulties in receiving the signal. However, GPS works in any weather including a thick cloud cover. Problems may only arise in very heavy snowfall.