Using array to list and list to array could possibly remove inner slashes, so you don't want to do that. Instead, replace leading and trailing slashes with a regex.
<cfscript>
string1 = "foobar";
string2 = "/foobar/";
string3 = "foo/bar";
string4 = "/foo/bar/";
function addSlashes (str) {
return "/" & reReplace(str,"^/|/$","","all") & "/";
}
writeDump(addSlashes(string1));
writeDump(addSlashes(string2));
writeDump(addSlashes(string3));
writeDump(addSlashes(string4));
</cfscript>
you can paste the above into http://www.trycf.com