I have heard the concept of softening up a Presidio by sending waves of marauders many but I believe this is wrong.

Here's why - 5000 mauds is about 200,000 attack force - a presidio defended with 20M results in a win/loss percentage of 20M/(0.2M+20M)= 99% loss of mauds and a 1% loss for all the troops at the presidio. The losses are applied to each troop type by pirate.

So If I am one of the crew with 45 subs & Nsubs, 45 GB & SOL 45 grenadiers, and 45 cuirassier defending the presidio the 1% goes against each of my troop types. 1% of 45 is .45% and I don't lose any troops but the attacker losses 99% - 45 of each reg defender is around 100,000 defense - 99% of 100K is 99,000 attacker force killed with no defender losses - this is almost half of the mauds sent and it is only one pirate defender - now image a 75 pirate crew defending against the maud raid- this is why mauds raids bounce off and hardly do any damage. The ones it does damage to are the defenders with a bunch of the same troop type - a pirate with 500 subs is going to lose 1% = 5 subs.

Two thing to take away from this - a bunch of mauds sent at a presidio is a bad attack strategy and second - structure your defense at the presidio to include as many troop types as possible with the same number of each type so that those that try to wear you down with mauds will be repulsed.

PS: the marauders are great they just need to be used correctly - mauds build force twice as fast as any other troop - you can build about 450 mauds per day and it has twice as much attack force as building as many bucs as you can. To use mauds they need to be coupled with other attackers so that you reach the threshold where the half a troop issue doesn't kill the attack.