Trigger with dynamic SQL

To avoid to delete registers I created one trigger activated "before delete"
with lines like that:
UPDATE tableX set dtExc = 'now', userExc = current_user where idTableX =
OLD.idTableX;
return NULL;

but, I need do the same for many tables and I don't catch how.
I created an sql variable to construct the update command using parameters
on trigger
qry := 'UPDATE '||arg_table||' set userexc = '
||chr(39)||current_user||chr(39)||', dtalt = '||'''now'''||' where ' ||
arg_id ||' = OLD.'||TG_ARGV[1];

but when "EXECUTE qry" I lost the OLD.variable.

I can't send the bigint id to delete in trigger parameters.

Any suggestions?

Thanks in advance,
Josi Perez