Yes I've done that already to an extent and didn't find way to remove this since 99% of time this transaction runs just fine.

Why I asked about the xlock select...

Yes that's true. I was wondering should I do select in the beginning of the transaction with all the participating hour Ids with xlock like:

SELECT * FROM [hour] WITH(XLOCK) WHERE...

Deadlock occures at the end of long invoicing transaction. First each hour row gets information about invoice from update. Lastly comes creation of invoice rows and these are updated to...