If you want to know the best place to train defence is in f2p? Once you have got def 69. First you could try cockroach soldiers in the Stronghold of Player Safety. You make a bit of cash from them, too. Just bring a full invent. of lobsters wearing full rune and you'll be there for a while making decent Runescape for not trying.
If you are level(runescape gold) 50 then you can choose the Giant Spiders (located in the third level of the Stronghold of Secrity), because there are level 50 and have 500 life points. They're also aggressive which makes it easier to train.
Aggressive and respawn quite quickly in Flesh Crawlers (located in the second level of the Stronghold of Security). The area usually isn't too crowded. You could also try Lesser Demons, they're level 81 and the bank is quite far away, although they sometimes have quite nice drops such as Rune med helms.
At last you could try Cockroach Soldiers in Runescape, they have quite high life points and a few very nice drops. However, they have very high defence and can sometimes deal up to 80 life points damage, and are often crowded.
