We have... all of the above

. We have 6 foot privacy fence along two sides - works great. We have chain link on one side, and I'd love to replace that with privacy fencing. Daisy doesn't jump it, but the neighbors on that side have three dogs, and when we go into the backyard, they all - my dogs and theirs - feel compelled to engage in competitive barking. Along the front (the part of the yard that faces the street) we have 4-5 foot picket fence similar to what was linked in the first post. Daisy can jump over it
easily, and if I were putting in a new fence, I definitely wouldn't go less than 6 feet if the doodle is a standard size.
What we did was 1) get an estimate on replacing the chain link fence and picket fence with 6-foot privacy fencing, and then 2) nearly faint at the cost and decide we couldn't afford it just then. Next we 3) strung a bit of clothesline along the top of the picket fence - enough to create a higher visual barrier for Daisy, which actually worked - she decided it was too high for her to jump. It sounds horribly tacky, but you can't actually see it from the street, and now that the shrubs have leafed out, you can't see it much at all. It helped during the winter though. The last thing we did was 4) buy this invisible fence -
http://www.petsafe.net/catalog/cart.php?m=product_detail&p=96&xc=16 - from Lowes, so that in case she did get out of the backyard, she wouldn't leave the front yard. It's a great product, I think - incredibly easy to set up, and if the dog does leave the yard, they
don't get a shock when they come back in. We have it set so that she can go anywhere in the backyard and within about 8 feet of the street in the front yard. We don't leave her out there unattended, but we love that we can have her out there with us when we're sitting on the porch or working in the front yard, and when we took her to the beach recently, I took her fence with us and was able to set it up at the beach house in just a few minutes; it made the week go much more smoothly! Anyway, I'm a big fan of a strong wooden fence, but I think this wireless product is a real improvement on the buried wire invisible fences, so I thought I'd mention it.
A lot depends on what you want the fence for. If you plan to leave the dogs outside unattended for long periods of time, then I think a wooden fence is the way to go. But if you plan to just let them out and keep an eye on them while they do their business, then the wireless fence is affordable and effective, at least with my Doodle

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S.