Is there a way to force a player's gamemode if they try to change it via /gamemode? So if they did /gamemode creative it would automatically put them back into survival?
Hm... do you want all players to always be on survival? Or just certain people? (Like, do you want admins?)
This will set everyone on creative to survival.
/gamemode @a[gamemode=creative] survival
If you wanted certain people to be able to go on creative, I would add a custom tag (/tag ExamplePlayer add Admin).
then you can set everyone on creative without that tag to survival with:
/gamemode @a[gamemode=creative,tag=!Admin] survival.
Please, everyone, if your post is solved, edit the name and mark it [SOLVED]. Period.