unique constraint

I have a table of paragraphs for pages that are in a specific order (1st,
2nd, 3rd, etc...).

demo=# \d paragraphs
Table "toolbox.paragraphs"
Column | Type | Modifiers

-------------+---------+---------------------------------------------------------
...
page | integer | not null
pos | integer | not null default 1
...

Is there a good way to ensure these paragraphs order can't get all out of
whack? what I mean is - we had a slight hiccup in a query and when
paragraph positions were moved it sometimes messed up the order of other
paragraph positions. for example, some paragraph positions for a page might
end up like (1st, 2nd, 2nd, 4th, 5th) or some other random list w/ duplicate
positions

I've fixed the incorrect query, but would like to know if there is a better
constraint that I could use to ensure this can't happen besides spectacular
bug-free programming

I tried using a unique constraint on the page/pos columns, but was running
into constraint errors when I did an update to move positions - in a
transaction, there might be two pages at the same position for an instance
while they are getting shuffled around.

to fix this I tried deferring the constraints, but as we're using version
8.2.5, realized this isn't supported and might not be the best approach?

Any ideas from the community that might be usefull?

Thanks,
Jamie K.