When I simply let my dog out to use the bathroom, she will always go normally without issue. 

The problem I am concerned about happens when we go on longer walks of about 2 mi. (3.2km). She stops *constantly* to try and poop. The first two to three times everything is normal and I have something to bag up... But she continues to try to go many more times after she has nothing left in her system. This will usually cause a mucus-like substance to excrete and it looks very unhealthy. On top of my health concerns, it can also be embarrassing for me to have my dog do the motions of going #2, and then I walk away without picking anything up - as she didn't actually go. My dog has done this on walks for the 7-8 years I have had her.

Once my dog's system is empty, should I hurry her along on my walk or allow her to try multiple times to go... when she can't?