The short answer is...yes those trails should be legal unless they cut ONTO perhaps a school property or cut through a police station, bar, or governing body's building.
Howver, I would caution you to rethink your plan to use a firearm against attacking dogs. Specifically multiple dogs as you've described. 2 or more large dogs charging you leaves you micro-seconds to react, draw, and come on line with mutiple charging targets with a center of mass disableing hit. That scenario equals multiple small area rapidly moving targets. VERY difficult to hit even one in the given short reation time under stress, adding multiple targets to aquire and hit, seems like asking for failure. And, once they're on you knawing on your arms/hands, your firearm would be useless.
I'mfar from aSelf Defense expert here, but, I'd say some form of chemical repellant even a solid bludgening walking stick to swingwould be more effective. just my humble opinion.