vents on a hip roof tall enough not to get buried by snow

My 1960s-vintage home has a hip roof--no gable to vent and built with no ridge vent. The roof has a 4/12 pitch. It has ample soffit vents and eight slant-back vents <http://www.owenscorning.com/around/ventilation/products.asp?ProdID &> spaced out near the ridge line. This works fine in the summer and most of the time in the winter. However, when a heavy snow buries the vents, I'll get ice dams if I don't get up on the roof and shovel out the vents.
We'll be installing new shingles this summer, and I'd like to solve the roof-venting problem at the same time. I've found three possible solutions so far. They're listed below, starting with the most expensive. Can anyone suggest other solutions or comment on the likely effectiveness of the ones I list?
Most expensive: One or two cupola vents. http://www.farmjonesbarns.com/cupolas.html http://www.castlecopper.com/html/cupola.html
Moderately expensive: gravity air vents with 12" stack Thaler Metal Industries http://www.partsdome.com/thalermetal/dept.asp?dept%5Fid 0 http://www.partsdome.com/thalermetal/dept.asp?dept%5Fid 5
Least expensive, least tall: square-hood vents with 6"-8" stack Owens Corning VentSure Square Hood Roof Vent with Large Base and Screen, High Stack http://www.owenscorning.com/around/ventilation/products.asp?ProdIDH
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Mike Bales wrote:

You're right, but I wouldn't have time to do that and still get the shingles installed while the weather is hot. Maybe someone knows of a mass-produced alternative that would suffice.

A compromise might be to replace only two or three of the existing vents --those in the part of the roof most susceptible to ice dams.

That's my worry, too. It would work most of the time, but I might still find myself heading to the roof after a heavy snow.
> Any reason why turbines wouldn't work?
I've considered installing two or three. They'd probably work, but I worry that neighbors might find them offensive. Do they rattle or squeak?

Right. Ridge vents work for neighboring houses that have steeper-pitched roofs, but it's clear they'd get buried on our shallowly-pitched roof.
Thanks for the suggestions.
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