You should probably add this line of css so that any images within a link do not show borders or underline.
.Logo a,.Logo a img{
border:none;
text-decoration:none;
}
Also as a side note, unless you have multiple logos you should probably use ID instead of CLASS as a best practice. You only use classes in css when there is the potential to have multiple elements needing the same styles.
Therefore making the code:
#Logo a, #Logo a img{
border:none;
text-decoration:none;
}