I would like to suggest set Dexcom G6 alerts to: (1) high at 160 mg/dl, (2) rise rate at 2 mg/dl/min. Once you receive the alert notification, start to walk immediately. If you don’t start walking, you may end up with high BG > 200 mg/dl.
If you plan to walk longer than 1 hour, consider reduce your breakfast bolus units, and set basal to zero at around 160-200 mg/dl for the remaining journey (2 hours+). You may still hit low BG (<80 mg/dl) later. In that case, consume some carbs around 100 mg/dl or so to prevent low BG.
You need practice and find out the best parameters to suit your need. Good luck.