Trying to find a straight line through the bush with an Etrex

Hello folks. Not sure if I'm in the right forum, but hoping someone can help out an old grey beard! I have a Garmin hand held Etrex, probably 7-8 years old. I'm trying to establish the property line at my cottage. I have found the 2 survey pins and made them waypoints. I stand over one and using the find menu, select go to the other one. My problem is between these 2 points is very thick forest. The property line is 450 feet long and I would like to make markers along this line. I'm sure I did this once but for the life of me I cannot repeat it. The way I remember it working was the black arrow stayed at the end of the line and the white arrow would follow the GPS. That way you could bisect the pink line several times and put some survey tape on the trees. I apologize in advance for the long post and the fact I probably on the wrong forum, but who knows, maybe someone can help an old guy out. Thanks very much for your time. Oh and go Vikings! Hope that doesn't cost me any help lol!