Battery kill switch

My GPS draws power all the time. I need to stop the power feed to the entire boat. Any ideas? 

If you want to stop all power just put in a battery switch. Perko is a popular brand and easy to install. 

https://www.perko.com/catalog/battery_switches/150/medium_duty_battery_disconnect_switch/

I know the "older" Lowrance systems with the independent puck system (LGC) antenna used to be a constant draw as it was not powered through the unit but by a separate power source in the NMEA backbone.

There are several ways to cheat and attach it to power supply that only is live with the ignition turned on but I found it easier to just install a simple little lighted toggle switch on the dash. I liked the lighted switch so even if I forgot the small glow in the garage reminded me. Its (the puck and the switch) draws VERY little power so forgetting it for a while isnt going to drain a battery either.

Several different methods already suggested, I'd go with the battery kill switch myself.  Easy turn of the switch.

Another thought...remove the fuse from the offending circuit when not in use. won't cost anything.

BFH, Do a search for "marine battery isolator/cut off switch". They are readily available from several sources i.e.; Amazon, Wal-Mart. West Mrine. Fleet Farm, Napa, etc. Insallation is usually simple. Lots of videos available if you feel the need for coaching. Amperage rating and style will vary based upon your application and needs. I'm willing to bet you're over qualified.

temp quick fix, just disconnect the power on the finder, unless it's a flush mount or some other hard to get at configuration

otherwise there's switches you can get examples