hi.
Are you trying to repeat lay at shortening odds whilst having an out bet at a certain lay price?
If this is the case, I would suggest you have a look at the following link, it is very informative about chasing drifters and steamers. You can certainly do what you have asked, I am sure some of the regulars on here will help.
newbielink:http://community.welldonesoft.com/triggers-for-learning/i've-made-(possibly)-profit-generating-triggers-guess-what-they-do-and-how!/msg18969/#msg18969 [nonactive]
Anyway, good luck