Candace Loses Her Head, I, Brobot

Phineas and Ferb decide to carve Candace's face into Mount Rushmore for her birthday present, while Perry attempts to stop Doofenshmirtz from making a tunnel to China.
Phineas and Ferb clone themselves so they can complete more projects while Doofenschmirtz hovers over his girlfriend's house with a huge magnet to erase crazy messages on her answering machine, for the sake of recording new ones.