Locking dimensions when resizing image boxes

I get very frustrated when I am trying to resize an image. I am obsessive about leaving a 1/4" gutter between pictures and using the same border size. When I am in edit mode and want to increase the top edge of the image box, very often the bottom edge also enlarges. Can I STOP THIS?  There is no way to increase or alter the pink guide on the template (a suggestion I highly recommend) and I can not just input the dimensions and location where I would like the image box to rest (another suggestion).  Can I LOCK anything so that only the edge I am trying to adjust moves?