When you are applying the show hide layer response you should be able to choose the triggering form element and for the layer you should be able to select the input from your form. If you do not see your input available it might be missing an id attribute, if this is the case you should make sure to add this in for each element on the page. All form elements should have a name and id, I usually use the same value for both of these attributes of an element.
I'm including a screen shot of what the behavior looks like on the example page, you should open this page in DW to get a feel for how the form and elements should be setup.
