The trick to this is that you have to have any surface a squirrel can grab be 6' off the ground. You also need the pole to be too wide for them to climb. To keep it affordable, I used PVC and a round HVAC duct pipe.
The biggest challenge is that if you are going that high, you still need to be able to reach it to get the seed in there, plus you obviously don't want it to be wonky. I had the additional challenge of needing to be able to easily dismantle it in case the landlord doesn't want it around whenever we move. So this version can be dismantled, leaving little trace behind.
**Make sure to plan to install this away from any tree branches or other obstacles that are within a 6' drop or 6' jumping distance.