I wouldn't spend time dynamically shuffling the order. Just log the "hits", and generate a new program every hour/week/month/whatever. Write the script like this:

while (<>) {
    s!http://www.theirsite.com/\W!http://our.server1/theirsite/\n!i   
+ ||
    s!http://www.theirsite.com/!http://our.server1/theirsite/|i ||
    s!http://www.dummy.com/\W!http://our.server2/dummy/\n!i ||
    ...
    logme ($&)
}
[download]

with logme an efficient log function. (And for those who want to complain about $&, think before you post).

Abigail