Specific Faction Strategies
GDIGDI will probably have the easiest time defending Tiberium fields, due to their larger amounts of garrisonable units as well as their sheer power. Because they do not have much speed, and instead act more like meat shields, it makes them perfect for defending the stationary Tiberium spikes. As vGDI, your most valuable asset is the APC, especially upgraded, as, even when un-upgraded, they still are extremely powerful against infantry and aircraft. But when upgraded, they are even strong against vehicles. Additionally, they can be garrisoned, with the preferred units being Zone Troopers, or Rocket Squads (depending on whether or not your enemy is using vehicles or aircraft). As for assaulting the enemy Spikes, it can be a great asset to have some Grenadier Squads with you to clear out any enemy bunkers.
Another great defender of Tiberium Spikes is, believe it or not, the Riflemen Squad. Their Dig in ability makes them the most valuable infantry unit that GDI has available, as then you can place any other infantry unit into the foxholes they make. This means that you have a garrisonable bunker to stick right next to the Tiberium field to defend against enemy Engineers or regular, non garrison clearing infantry. However, the bunkers that normally surround a Tiberium Spike are normally better for garrisoning than Foxholes.
The Dig in ability Try using infantry in more of a supporting role (except for the Riflemen's Foxhole) when fighting for the Spikes, as a legion of infantry can be slaughtered by a large number of anti infantry units. Therefore, it is best to have them supported with vehicles as well. The Pitbull is great for this task, as it will obliterate any aircraft that dare come near your Spike. Additionally, Predator and Mammoth Tanks (especially upgraded) make great support units as well. Make sure that you micro them correctly in order to attack enemy units from behind and from the side.
A Picture of the Dig in AbilityFast attack aircraft (for example Hammerheads) make great defenders and assault units. Because they are so fast, and can also be garrisoned, they can be extremely useful for swooping in, taking out any defenses with their AP ammo rounds, clearing out any bunkers with their garrisoned Grenadier Squads, and then land an Engineer to capture the spike.
Lastly, the Rig makes a terrific defense against enemy vehicles, can be repaired and can support your vehicles with repairs. It is cheap and mobile, and is very effective.
The Rig Defending a SpikeThe only really special aspect about ZOCOM is that their aircraft can be upgraded with Ceramic Armour to increase their hitpoints. This makes the Hammerhead much more useful in this situation. Additionally, they have access to the "great against everything" Zone Raider.
The lack of Railguns is a considerable loss, however, and you'll need to supplement that with higher numbers of tanks and APCs. Make sure the APCs are upgraded though. Defending the spikes as ZOCOM might be considerably harder than with the other factions.
Steel TalonsThe Steel Talons have access to the steamrolling type units. Two of the most important of these are the Titan (the substitute for the Predator) and the Wolverine (the anti infantry, and vehicle unit, at least when upgraded). Not only this, but the Titan can also crush tier one infantry and vehicles. This makes it extremely potent when being assaulted and assaulting enemy tier one units. Simply use your other units as support, and send your Titans to squish all enemy early game units.
The MRT (Mobile Repair Transport) can not only transport and garrison units inside of it, such as the Combat Engineer or the other infantry, it can also repair nearby units, and itself. This makes it a critical part of any Steel Talons army.
The Steel Talons also have the most garrisonable units of any faction (the MRT, Hammerhead, Heavy Harvester, and Behemoth). This means that they have the most functionality when it comes to sticking engineers inside units and sending them to capture Spikes. If you defend a Spike with a Behemoth or two, you can even stick an engineer inside it and unload it to capture the spike. It gets even more versatile. As you can even send a Heavy Harvester with a Combat Engineer inside it past the enemy Spike. They will probably just mistake it for a normal Harvester, and wait for it to get to its field so they can kill it. But then you can surprise him or her by unloading the Combat Engineer, and capturing the Spike without them even knowing about it.
