Depending on what glue it is, use:
Mineral Spirits
Lacquer Thinner
Acetone
Isopropyl alcohol
Denatured alcohol
epoxy remover
3m 5200 remover
xylene
Anhydrous ammonia
And finally hard work or heat, some glues are not soluble in anything you would want to touch your boat. The last 4 in my list should be tried on boats with extreme caution. They could soften if not remove gelcoat
The best stuff I have found is 3M decal or IPS decal remover. The formulation changes, they put a little bit of everything in it.
My preferred method is to use mineral spirits, then acetone, next 3m decal remover and finally a heat gun at no more than 200F
This is just going to get worse over time. I have seen new product announcements, that are really inert adhesives that use 10-100 ppm of acid on their surface to chemically bond to whatever you put them on. That's going to suck to get off.
