Many times you'd only use a simple past, the context will make it clear whether it's a plusquamperfectum or not; the words もう/すでに make the meaning clearer. The structure past + ことがある is used to talk about experiences, usually the word 'ever' is appropriate to use when translating. Have you ever gone to a karaoke?, Have you ever eaten okomiyaki?, Have you ever felt so bad you'd punch a dwarf in the face?, I've never eating a rabbit. You'd use ことがある in all those examples. (although I've never done X thing can be also usually rendered as ～のは初めてだ, though).
However, in your example, with some more context it is possible to use ～ことがある. For example, if somebody asks ''have you ever been with somebody in a forest?'', the answer can be like your example. But if the sentence is not talking about experiences a simple past will suffice, sometimes a past continuous will also help, it depends on the action. For example, here:
When my mom came back I had already eaten. 母が帰ってきたとき、私はもう食べてしまっていた/食べ終わっていた。
パリに引っ越す前に、私は3年間香港に住んでいた。I had lived for 3 years in Hong Kong before I moved to Paris.
I hope this helped.
Last edited by 涼宮; 20th March 2013 at 8:21 PM.
Username: Suzumiya. 所詮この世は弱肉強食。強ければ生き、弱ければ死ぬ。-志々雄真実