If he has no legal cause to retain your deposit (and I had 1 out of 4 landlords I used who retained part of my deposit without good cause) then he is a disgrace to his fellow citizens and a sh*t.

 

Does anyone know of these types of 'funnel traps' for trapping fish so that they can get in easily but have a problem getting out again?

Sounds off-topic (but hold onto your sword a minute @Rye83) - this is the same for cash here. Easily goes in to another's pocket but a hell of a job getting it out again.

 

Private enquiry agent? I am sure you do Know and they have a way of leaning on people a lawyer would not, as to the small claims court there will be costs to that as well, the DTI is not a way I would go given they rarely achieve promises to the small man,
Unless the Landlord has prior problems like this I can't see a Legal way to get the Deposit back without it costing BUT I wonder if the OP has approached the Barangay Captain? In issues like this they can be useful

 

For me, I would write if off, it could cost that amount and more to do what you ask, JMHO but if it went to court ( and it might) you will find it 10.000 to lodge the Complaint and around 4/5000 a day in Hearings, with no guarantee of a win, Costs don't usually get awarded so it may well all fall on your Shoulders, A private enquiry agent might suit better