We were discussing this at the field yesterday. Basically most of the ARFs people acquired recently (regardless of big name brands or knock-offs) have varying levels of issues with their monokote covering coming off.  Some times it is the decals that come off first.

What are the solutions usually employed for this ?  Frequent ironing ?  Some kind of varnish applied ?  Diluted glue ?

During one of my discussion on the field some one suggested to put a thin layer of clear varnish along the edges/joints to avoid pealing of stickers and monokote. But never tried that, I usually iron them until they stop sticking and then uses clear tape. I am not sure if the clear varnish will hold if the plane is with nitro engine.

This is a very common occuring phenomenon. The cheaper quality films are more sensitive to heat and shrink/bubble very easily in the sun. Earlier I have used a very fine coat of "clear" coating on my balsa models. It works well. You need to dilute it with methanol and then just brush. However the shade of the color of the model changes...  a very light pale yellow color from milky white.
But later I realised it was not worth the pain... Its best to stick with some cello tape/fibre tape when the film peels off. Hair-dyer at home works good for loose skin.

Mike applies clear varnish on his solartex covered planes, so clear varnish itself seems to be safe from nitro fuel.  Question is, whether the same applies to monokote.  Solartex is a different type of material (more like cloth/canvas), and is grey in color (guess that is Mike's choice of color).

I think Solartex is more thicker and heavy than monokote. My Mustang was covered with solartex and the colour was silver or Gray. I foud it more durable than monokote.

Yes, Solartex is much more durable.