Well, I trained at white knights castle at falador, it's safe and with my 75 str and 70 attack i had 230k xp hour there, so it's pretty decent.
And if you have dragon defender just collect few mates, get loads of tokens and go down to basement to kill cyclobs who drops d defenders, nuts xp there, iI got almost 300k xp hour! and it's pretty safe tbh, just getting tokens can be a pain.