Code:

on *:JOIN:#:{
if ($nick == $me) { 
%topic $+ chan = $chan(#).topic
}
}

on *:TOPIC:#:{
if ($nick == $me) { 
timer 1 3 /set %topic $+ chan $chan(#).topic | halt
}
else { topic # %topic $+ chan }
}


or just //mode # +t

and theres your topic lock