Trying again....get along with the PRC and the US.  As they maintain a small presence in the region, try not to anger the French.

 

M-08/39 mines...and claim that if they invade you, whosever is "they;" Somalia will revert back to the chaos it was before your rule...trust me no one wants that and that's one of your better defenses.

You'd have to start from the ground up and keep major enemies off with diplomacy...start with a Coast Guard?

Being good Moslems and proven Islamic militants, the new regime immediately open channels to brethren in (where else) Iran. Through shell companies and the intricacies of foreign money laundering, limited funds and weaponry start to flow into the country. This is a very viable scenario that's been gamed in the open and to a limited extent at the various War Colleges.

 

Just to put the scenario into perspective, the Somali Basin shoreline alone is over 2,000 miles long. Assuming you had to defend to a reasonable depth to trade space for time (150 miles), that's 300,000 square miles. Between that and the coastline facing the Gulf of Aden, not all of it is suitable for an amphibious assault landing; there are only about 12 coastal towns or cities that link back into the country's questionable road infrastructure in order to quickly move troops and supplies. You'd have to prioritize your limited funding to bolstering areas like Mogadishu, Eyl or Boosaaso - places that have a deep enough draft and port facilities to allow amphib and troopships to unload easily.

 

The best strategy would be to employ a layered defense on land, making it very expensive for the assaulting forces to make progress into the main cities. It's likely you do not have a sufficiently large cadre of technical personnel or equipment to make a stand against the amphibious landing. In essence, you are giving up the ability to smash a landing and preserving your combat power for the area where you can excel - making the occupation (even temporary) of the mainland a protracted land war. This dials into the current Western appetite against such an undertaking.

 

Now, the spin would be, what if no one cared that there was a change in regimes within Somalia? What would one do legitimately do to protect your coast and immediate sea areas? Again, assuming patronage of an outside state, your immediate options are to set up some sort of Coast Guard. The wildcard factor is this - are the pirate havens with you or not?  You could set up the pirates themselves as the Coast Guard of sorts, but what to do about their piracy activities? Allowing them to continue would be simply a state endorsement of what's already considered criminal activity - thereby making them a CG in name only, not in function. If they're not with you - does it make more sense to cease all activities by the pirates or do you allow them to continue, knowing they're causing more trouble for your opponents than you?

Coast watchers are a job for the civilian militia.  Use the regular phone net, carrier pigeons are too slow to provide target data.  In fact, with a top speed of 60 mph (100 kph) the attacker may occupy your headquarters before the message arrives.