We would probably need to know more. For example, how are your collisions set up in general? How is your movement set up? Seeing the code for that would likely get a better answer. However, the start of your question - objects that surround the map, also make me think that maybe you want some kind of border, that might be easier to do just by clamping (see the clamp function in the manual) the x and y values of whatever object you want to the room boundaries (e.g. 0 and room_width for x and 0 and room_height for y).
I think this is the second post I've seen you use one of the ev_ constants in a completely wrong manner. You should read the manual again (you did read it before right?) to pick up on the basics. You are fumbling in the dark if you randomly pick using something like ev_boundary is a clamp expression. It makes zero sense.
Either of those should work, and that is the proper use of clamp (the first post was not as chamaeleon noted). Are you saying you tried those and those also did not work? If so, then I would check to see whether the code is running or whether there is anything interfering with it.