There's a fishermen's marina in Vieux Fort, protected by a breakwater--look it up on Google Earth
. You can't go into the marina, but holding is good outside the breakwater. As atoll says, it can be a bit choppy. I stopped there to drop off crew who were flying home and pick up my wife and cat, who had flown in on the plane my crew were flying back to the States on, leaving the boat unattended for two hours or so.
into the marina, but be careful where you park it. It's been some time and my memory is a bit cloudy, but I seem to remember being told to tie up outside a fenced area within the marina, off to the right of the buildings somewhere. I was approached by a kid and an adult male, each wanting to "guard the dinghy" for a fee. I struck a deal with the adult--$5 EC ($1.86 US). The kid was miffed, so I gave him a candy bar, which was OK with him. Lock the dinghy
; pay the dinghy guard when you come back. You can find a taxi in town, and it's a short ride to the airport terminal.
There have been some instances of boat burglaries in the anchorage there, but I would imagine you'd be OK leaving it for a couple of hours during the day. Lock up tight if staying overnight.