Dave:
I experienced the same problem and bought the Orvis Uniform Sink line that has the tip end slightly heavier than the rest of the line so that the line doesn't form a belly from the tippet & fly trying to float that end of the line.
I also use Depth-Charge lines, but prefer the Teeny versions for some unknown reason (never had one fall apart as others have alluded the D-C's to do, maybe that's why?). I find them an ideally slotted between intermidiate & the bottom-dragger lines.
Where I flyfish about 70% of the time from a boat & usually in rips or other current, I rarely use an intermediate - 'cause in those conditions it instantly becomes a "floating" line.