I was wondering if there was someway to lock an attribute such as y in a way that I could move any part of the object above y=o but not below

so basically I want to set it like this y>0

except greater than or equal to lol (don't know how to make that symbol)

If you are confused let me know and I'll see if I can explain it better

I'm deforming an object and I want to be able to move part of it down and up, but not below the grid (y=0) that is my reason for this question

also I do know how to lock certain attributes, but that does not allow me to move it any direction in y, I want to be able to move it any direction except below 0

Sorry for the confusing explanation, any help would be appreciated thanks!