Best way to slow down trolling speed?

I have a wonderful Sylvan 17'8" with 90hp Evinrude Ficht. Love the combo. Need to slow down my trolling speed. I drag a windsock, but think there should be a better way. Trying to avoid the kicker motor if I can. Anyone use the trolling plates I see advertised in Cabela's? I have prior experience with the spring loaded models that pop up when you go fast. This is not acceptable as you lose too much control at slow speed. Reverse gear is dangerous in a close quarters situation. I see a model that has a string attached, actually a steel cable, to raise the plate, therby taking it out of the action. Seems like a good idea. Any comments? I'll do the kicker if I must, but would like to avoid the $.

Thanks in advance.