I had the same issue with zip ties – just too inconvenient to open up the cage for regular maintenance – so I use a slightly different method that I’ve slowly developed over years, which dispenses with the t-posts entirely.
Imagine that the cage makes a circle with 0 degrees at the point where the edges meet. I secure the cage into the ground with three pieces of J-hook rebar driven in at 90 degrees, 180 degrees, and 270 degrees (see the blue arrow in the picture below). The ends of the cage at 0 degrees are then fastened together with three cheap aluminum carabiner clips (yellow arrows). Here is what it looks like:
It might not be beautiful, but it’s simple to set up, allows great access for maintenance (disconnecting the carabiner clips takes seconds and lets the whole front open like a door) and the whole setup can be dismantled swiftly. I’ve been using it for years and it is effective at keeping out the deer – and they definitely try to get through.