You could slide your new airline inside 1" plastic water line to act as a "conduit." You might end up having to add weight to get the combined lines to sink - I can't remember if I had to weight the 1" plastic line in my pond or not (for livestock water, not conduit for the airline).

If you really think it's the beavers, I think you'd be ahead with a good offense,

"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
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