How much tension should there be in the lines?
The more tension, the better.
If a bear tries to enter your camp site, the Bear Sentry energizer is highly capable of delivering the shock to deter it. However, you’ve got to provide the best circumstances for that big shock to happen: make sure the system is operating properly (see the FAQ) and reduce sag in the lines.
The best and more likely scenario has the bear touching the polywire with its wet nose; the electrical connection will be relatively easy.
Your Bear Sentry does have the high voltage potential or “electrical pressure” to get through long and thick fur to the skin for a shock (see the FAQ). However, it will help if the line penetrates the fur in the first place, physically, and this requires some tension in the line.
So watch for ways to make your Bear Sentry as robust as it can be. This includes tensioning the polywire with guylines.
Bear Sentry guylines are available with More Good Kit.