Your link states: the can has to close perfectly, and you will have to line the walls with cardboard... It is best to use metal tape to seal the lid and to help make sure the lid does not work loose; also best if the can is grounded, even better if buried.
A good introduction to what an EMP is is available here, with many further links.
Wikipedia also has a page about faraday cages.
I have a faraday cage - an old Navy equipment carry case made of aluminum. One thing I note is to replace stored batteries more often than I have. When I finally rotated stock the batteries had lost about 20% of their power.
An ex-active FReeper in Sarasota has/had a faraday room with plenty of 'puter stuff and a bunch of terabytes of memory storage. He also had a surplus military diesel SUV that he said was guaranteed to start and run in case of an EMP.
It is important also to mention that we are basically talking here of a nuclear EMP attack. It is possible for strong solar flares - solar geomagnetic storms - to create a damaging EMP pulse. A very strong geomagnetic storm could knock out our electric power grid - a potential national disaster. In 1859 a large solar-caused geomagnetic storm known as the Carrington event knocked out all telegraph lines in North America and Europe. {link worked the first time, not since - ?}
Another worry. 😎
Bob why are we talking about EMP’s? Was there a threat that I missed?