Silt control, who's problem?

So who's to pay for Silt control to go in when the dirt that is washing down onto us is partly from sold blocks and partly from unsold blocks?

This conversation started when our supervisor had 1 look at our block and said "you need to get Delfin to put some silt control up at the back and on 1 side to stop the blocks behind and next to us that are higher having all their dirt run off onto ours in any rain. Metricon obviously pay to do the front to stop dirt going onto the road but the back usually isnt done. Delfin dont want to pay as they say "if we do it for 1 we have to do it for all" (as they should have in the first place seeing as they dont turf their sites to stop the run off in the first place!) and Metricon will only bill us as its not allowed for in their contract.

Anyway, now the only choice I see is that we'll have to fork out the $ to do this. The consequences of not doing it are:

1. it rains and the dirt runs off the higher blocks down onto ours
2. there ends up being damage done to our slab or site cut due to the water and excess dirt
3. the site ends up so muddy they cant work, and
4. they cant work so our finish date gets held up!

The only reasonable answer to all this I can see is for us to fork out this $ (possibly about $400) to stop any of these problems happening, pity the DH doesnt agree we should pay so now i'm left fighting with everyone over what to do! Grrr, and the stress begins and they havent even started building yet! :(