I was going to suggest junipers also. Arborvitae might work but are not as wind tolerant. I'm assuming you want a cylindrical tree not a cone shaped tree. To get the density, you might plant 2 rows, 3 feet apart, with the trees spaced 6 feet apart in the rows. The rows would be offset so if you looked at the hedge, you would see a tree every 3 feet. I suppose that plan depends on how much space you have.

Thanks for the suggestion. What about Green Giants? They are a bit cheaper, and just as easy to control the height, as long as they are trimmed. They can grow 2 - 3 feet a year, however, can they withstand the green bay winters? We haven't experienced one yet, so we don't know what we're up against...

Thuja 'Green Giant' is a hybrid between Thuja plicata and Thuja standishii and zone 5 is about their limit, I believe. Do you know of any 'Green Giants' growing in Green Bay? You may also need to consider how salt tolerant the plant is if it can be sprayed by passing snow plows/car splashing. Junipers are generally considered more salt tolerant than Thujas are and since they are more "prickly" they may make a better fence as well.

tj