Burdokva said:
Also, a dictator isn't an evil space wizard. They should have sensed the Force being strong(ly evil) with him. ;)
All they had to do is have Palpatine say "I masked my presence" or "I didn't use The Force when the Jedi were present" to Anakin.
Interestingly,the Jedi not sensing anything about Palpatine was one of the justifications for the Palpatine is a clone of Sidious theory.