A lot of school districts have implemented some form of website blocking. Unfortunately, valuable teaching sites are blocked. I've found several ways to keep blocking from stopping me.
The first way is to have a phone that tethers. Tethering is the term for attaching a mobile phone to a computer, thus allowing the computer internet access. You can do it with either cabling (mine uses a USB cable), or Bluetooth. Unfortunately it is often an extra charge, but at the same time, being able to tether protects YOU!. I often want to do non-work related activities during lunch or my planning period, and tethering allows me to do it legally. Frankly, having the ability to tether has kept me a little more sane in a lot of non-campus situations, so it's worth it to me. Think about it, as long as you have mobile phone access, you can tether.
The second way is to use some form of web page capturing. I usually use Adobe Acrobat reader. Anytime I see a website I want to use later in class, I put it in a PDF and save it. That protects you from a lot of things besides blocking. You can save just the webpage without the advertising, especially if the advertising isn't exactly what your students to see. You can also make notes on it or highlight sections. It is also helpful is the internet itself is down, as you can retrieve it and display it with your projector. Or even worse, kill a tree and print it out -- something I hate to do, but occasionally everything is failing -- for exapmle, we had a school day where we started without power, recently.
I don't like to use a proxy, as I believe you are teaching your students to do something dishonest. In fact, a well written Acceptable Use Policy will specify that you and your students are NOT to use proxies. I will admit to using one in an extreme emergency -- at the end of the six weeks and the district had blocked my personal website so students couldn't turn in work.