NEIGHBORS ON MY DHCP

Hey, recently I've been having some problems i thought was associated with an insecure wireless network I set up.
Lately I've been noticing my neighbors jumping onto my connection, i've filtered they're mac ids, and kicked them several times, they're connection though, is on my DHCP clients table in my router and not on my wifi, what the hell does that mean? are they hardwired somehow, my router does not show anyone besides me and another computer connected (ie blinking lights) but in the server it still shows they are connected. I've looked around and there are NO wires running from my house or roof so wtf?? I don't get this and how can i get these nigras off it's bad enough they stole my bike, now my internet?? I don't think so Please help me!

i just switched to wpa-psk with aes encryption using letters and numbers 20 characters long with keyrenewal ever 3600 seconds(might  bring that down a little any problem changing it sooner than longer?) they must be on my wifi even though for some reason they're not showing up on my wireless client table and instead my dhcp client list. I haven't had them on for a couple hours (since I kicked them last) I also disable my wireless while I set up my passwords to prevent them from snopping (thanks to /g/) and so far so good i suppose but sometimes it takes them up to several days to jump back on, especially since I've been changing my passwords daily and kicking them just the same. I don't know what else to do If they DO end up jumping back on.