There are 2 main things that will shorten shock life significantly.

The first is damage to the exposed shock rod and the rod seal. Dust and dirt settle on the rod, and as it retracts into the shock body during compression, the rod seal needs to wipe it off. This wears the seal over time and eventually your shock leaks. Rocks hitting the rod also cause scratches and pitting, and these imperfections also wear on the seal each time they slide past. You want to do everything you can to keep the rod clean. OE shocks of any style usually come with a boot, so this is why they tend to last longer. Most aftermarket shocks like Icon, King and Fox don't. You can add an accordion sleeves to shocks or a coilover sleeve to coilovers to help with this and I highly encourage it.

The second is overheating which also causes damage to the seals, both internal and external. The best defense against this is an external reservoir. Reservoirs help in 3 main ways.

1. They increase the oil volume, so it takes longer for it all to heat up.

2. They increase surface area, so they help with cooling the shock oil a bit

3. The extra gas chamber volume helps reduce the operating pressures inside the shock. The lower pressures also help the seals last longer.

What kind of shocks you need really depends on your application.

For low speed rock crawling just about anything will do, but make sure you add shock and coilover sleeves to maximize life.

If you drive fire roads or anything where you get up to 40 mph for longer than a few minutes at a time, you want the remote reservoirs.

This tech article talks about it a little.

Emulsion vs Reservoir Shocks: Learn & Save | AccuTune