Hi All
Rman
I'm still working on my One Gauge layout and came up with the same problem your discussing. Due to the fact I have several hundred figures and accessories that I will be using out side to enhance scenery and buildings so it's important to me they stay where I put them.
I have used numerous adhesives like the examples that are already posted for my inside layout and there good.
Recently I experimented with a different product that has really impressed me . I obtained it from Michael's. Called Glue Lines and Glue Dots. Both inexpensive and may surprise you with the adhesive ability.
I'm going to use it outside. You can cut the little circles or strips however you want to use them for getting a piece small enough for people ect.
It really STICKS but comes off easy in the event you want to remove it.
Here are pictures.
SEE this little guy in the last two pictures. I placed him on the flat rock over a month ago. Even after VERY heavy rains and storms he's still standing and secure.
Larry