turtles are insecure animals and need a place to hide otherwise they become unhealthy due to stress.
its a common misconception that turtles are low maintenance pets. turtles require a day/night cycle. they require clear separation between dry land and water, because they are cold blooded creatures. they go in the water when they are hot and come out when they are cold. they require heat lamps to stay warm outside of the water. they require filtration to keep their water clean. in the wild this isnt a big problem but in a tank it is, their swimming water is also their drinking water. if you have a high volume tank, your water will need a heater to maintain temperature. and most importantly they require a cave or a log or something in the water to hide.
preventing your turtle from hiding is extremely unhealthy for your pet. your turtle is only insecure because his environment is not suited for him. if you provide an adequate habitat for him he should be confident enough to stick his head out more often.
you should NEVER glue ANYTHING to a living animal.
also, wash your hands after handling your turtle, they are covered in salmonella.
Turtle raising experience.