This will work fine but im sure it wont be cheap. 12 guage has a current carrying capacity of around 30 amps, so depending on the load, the voltage used (5v or 12v) and the distance then you may be spending more on cable than you need to. But this will work very well and give very little voltage drop compared to other alternatives.
14/0.2 4 core security cable is 0.5mm^2 per core. Double these up and you have 1mm^2 which should be good for about 10A.
I use some 0.75mm^2 figure 8 which works fine.
Some quick figuring, for injecting at least every 10m. A 10m segment is ~75W or ~6A total for 30LEDs per meter strip. Also bear in mind that it is powered from the data end as well as every injection point. This means the limiting factor isn't your power cable, it is more the strip itself. 1mm^2 over 10m at 3A will drop about 1V which is fine.
Of course if your doing massive cable runs then resistance might me an issue.