I wouldn’t use checkboxes, i’d use the code you already have
DEMO http://jsfiddle.net/6W7XD/1/
CSS
body {
display: block;
}
.span3:focus ~ .alert {
display: none;
}
.span2:focus ~ .alert {
display: block;
}
.alert{display:none;}
HTML
<span class="span3">Hide Me</span>
<span class="span2">Show Me</span>
<p class="alert" >Some alarming information here</p>
This way the text is only hidden on click of the hide element