Blocking on its own is easy to get around. What makes this work is that someone you trust is told when a blocked site gets reached for — and told if this extension gets removed.
Paste the pairing code from your account page. It's how Shield knows which subscription it belongs to.
Pick someone who already knows you're working on this. A person who will be kind about it and won't let it slide.
chrome://extensions — Chrome won't let us do that for you.